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  • What Is a Case-Control Study? | Definition & Examples

What Is a Case-Control Study? | Definition & Examples

Published on February 4, 2023 by Tegan George . Revised on June 22, 2023.

A case-control study is an experimental design that compares a group of participants possessing a condition of interest to a very similar group lacking that condition. Here, the participants possessing the attribute of study, such as a disease, are called the “case,” and those without it are the “control.”

It’s important to remember that the case group is chosen because they already possess the attribute of interest. The point of the control group is to facilitate investigation, e.g., studying whether the case group systematically exhibits that attribute more than the control group does.

Table of contents

When to use a case-control study, examples of case-control studies, advantages and disadvantages of case-control studies, other interesting articles, frequently asked questions.

Case-control studies are a type of observational study often used in fields like medical research, environmental health, or epidemiology. While most observational studies are qualitative in nature, case-control studies can also be quantitative , and they often are in healthcare settings. Case-control studies can be used for both exploratory and explanatory research , and they are a good choice for studying research topics like disease exposure and health outcomes.

A case-control study may be a good fit for your research if it meets the following criteria.

  • Data on exposure (e.g., to a chemical or a pesticide) are difficult to obtain or expensive.
  • The disease associated with the exposure you’re studying has a long incubation period or is rare or under-studied (e.g., AIDS in the early 1980s).
  • The population you are studying is difficult to contact for follow-up questions (e.g., asylum seekers).

Retrospective cohort studies use existing secondary research data, such as medical records or databases, to identify a group of people with a common exposure or risk factor and to observe their outcomes over time. Case-control studies conduct primary research , comparing a group of participants possessing a condition of interest to a very similar group lacking that condition in real time.

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case control studies in research

Case-control studies are common in fields like epidemiology, healthcare, and psychology.

You would then collect data on your participants’ exposure to contaminated drinking water, focusing on variables such as the source of said water and the duration of exposure, for both groups. You could then compare the two to determine if there is a relationship between drinking water contamination and the risk of developing a gastrointestinal illness. Example: Healthcare case-control study You are interested in the relationship between the dietary intake of a particular vitamin (e.g., vitamin D) and the risk of developing osteoporosis later in life. Here, the case group would be individuals who have been diagnosed with osteoporosis, while the control group would be individuals without osteoporosis.

You would then collect information on dietary intake of vitamin D for both the cases and controls and compare the two groups to determine if there is a relationship between vitamin D intake and the risk of developing osteoporosis. Example: Psychology case-control study You are studying the relationship between early-childhood stress and the likelihood of later developing post-traumatic stress disorder (PTSD). Here, the case group would be individuals who have been diagnosed with PTSD, while the control group would be individuals without PTSD.

Case-control studies are a solid research method choice, but they come with distinct advantages and disadvantages.

Advantages of case-control studies

  • Case-control studies are a great choice if you have any ethical considerations about your participants that could preclude you from using a traditional experimental design .
  • Case-control studies are time efficient and fairly inexpensive to conduct because they require fewer subjects than other research methods .
  • If there were multiple exposures leading to a single outcome, case-control studies can incorporate that. As such, they truly shine when used to study rare outcomes or outbreaks of a particular disease .

Disadvantages of case-control studies

  • Case-control studies, similarly to observational studies, run a high risk of research biases . They are particularly susceptible to observer bias , recall bias , and interviewer bias.
  • In the case of very rare exposures of the outcome studied, attempting to conduct a case-control study can be very time consuming and inefficient .
  • Case-control studies in general have low internal validity  and are not always credible.

Case-control studies by design focus on one singular outcome. This makes them very rigid and not generalizable , as no extrapolation can be made about other outcomes like risk recurrence or future exposure threat. This leads to less satisfying results than other methodological choices.

If you want to know more about statistics , methodology , or research bias , make sure to check out some of our other articles with explanations and examples.

  • Student’s  t -distribution
  • Normal distribution
  • Null and Alternative Hypotheses
  • Chi square tests
  • Confidence interval
  • Quartiles & Quantiles
  • Cluster sampling
  • Stratified sampling
  • Data cleansing
  • Reproducibility vs Replicability
  • Peer review
  • Prospective cohort study

Research bias

  • Implicit bias
  • Cognitive bias
  • Placebo effect
  • Hawthorne effect
  • Hindsight bias
  • Affect heuristic
  • Social desirability bias

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A case-control study differs from a cohort study because cohort studies are more longitudinal in nature and do not necessarily require a control group .

While one may be added if the investigator so chooses, members of the cohort are primarily selected because of a shared characteristic among them. In particular, retrospective cohort studies are designed to follow a group of people with a common exposure or risk factor over time and observe their outcomes.

Case-control studies, in contrast, require both a case group and a control group, as suggested by their name, and usually are used to identify risk factors for a disease by comparing cases and controls.

A case-control study differs from a cross-sectional study because case-control studies are naturally retrospective in nature, looking backward in time to identify exposures that may have occurred before the development of the disease.

On the other hand, cross-sectional studies collect data on a population at a single point in time. The goal here is to describe the characteristics of the population, such as their age, gender identity, or health status, and understand the distribution and relationships of these characteristics.

Cases and controls are selected for a case-control study based on their inherent characteristics. Participants already possessing the condition of interest form the “case,” while those without form the “control.”

Keep in mind that by definition the case group is chosen because they already possess the attribute of interest. The point of the control group is to facilitate investigation, e.g., studying whether the case group systematically exhibits that attribute more than the control group does.

The strength of the association between an exposure and a disease in a case-control study can be measured using a few different statistical measures , such as odds ratios (ORs) and relative risk (RR).

No, case-control studies cannot establish causality as a standalone measure.

As observational studies , they can suggest associations between an exposure and a disease, but they cannot prove without a doubt that the exposure causes the disease. In particular, issues arising from timing, research biases like recall bias , and the selection of variables lead to low internal validity and the inability to determine causality.

Sources in this article

We strongly encourage students to use sources in their work. You can cite our article (APA Style) or take a deep dive into the articles below.

George, T. (2023, June 22). What Is a Case-Control Study? | Definition & Examples. Scribbr. Retrieved February 22, 2024, from https://www.scribbr.com/methodology/case-control-study/
Schlesselman, J. J. (1982). Case-Control Studies: Design, Conduct, Analysis (Monographs in Epidemiology and Biostatistics, 2) (Illustrated). Oxford University Press.

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Study Design 101

  • Helpful formulas
  • Finding specific study types
  • Case Control Study
  • Meta- Analysis
  • Systematic Review
  • Practice Guideline
  • Randomized Controlled Trial
  • Cohort Study
  • Case Reports

A study that compares patients who have a disease or outcome of interest (cases) with patients who do not have the disease or outcome (controls), and looks back retrospectively to compare how frequently the exposure to a risk factor is present in each group to determine the relationship between the risk factor and the disease.

Case control studies are observational because no intervention is attempted and no attempt is made to alter the course of the disease. The goal is to retrospectively determine the exposure to the risk factor of interest from each of the two groups of individuals: cases and controls. These studies are designed to estimate odds.

Case control studies are also known as "retrospective studies" and "case-referent studies."

  • Good for studying rare conditions or diseases
  • Less time needed to conduct the study because the condition or disease has already occurred
  • Lets you simultaneously look at multiple risk factors
  • Useful as initial studies to establish an association
  • Can answer questions that could not be answered through other study designs

Disadvantages

  • Retrospective studies have more problems with data quality because they rely on memory and people with a condition will be more motivated to recall risk factors (also called recall bias).
  • Not good for evaluating diagnostic tests because it’s already clear that the cases have the condition and the controls do not
  • It can be difficult to find a suitable control group

Design pitfalls to look out for

Care should be taken to avoid confounding, which arises when an exposure and an outcome are both strongly associated with a third variable. Controls should be subjects who might have been cases in the study but are selected independent of the exposure. Cases and controls should also not be "over-matched."

Is the control group appropriate for the population? Does the study use matching or pairing appropriately to avoid the effects of a confounding variable? Does it use appropriate inclusion and exclusion criteria?

Fictitious Example

There is a suspicion that zinc oxide, the white non-absorbent sunscreen traditionally worn by lifeguards is more effective at preventing sunburns that lead to skin cancer than absorbent sunscreen lotions. A case-control study was conducted to investigate if exposure to zinc oxide is a more effective skin cancer prevention measure. The study involved comparing a group of former lifeguards that had developed cancer on their cheeks and noses (cases) to a group of lifeguards without this type of cancer (controls) and assess their prior exposure to zinc oxide or absorbent sunscreen lotions.

This study would be retrospective in that the former lifeguards would be asked to recall which type of sunscreen they used on their face and approximately how often. This could be either a matched or unmatched study, but efforts would need to be made to ensure that the former lifeguards are of the same average age, and lifeguarded for a similar number of seasons and amount of time per season.

Real-life Examples

Boubekri, M., Cheung, I., Reid, K., Wang, C., & Zee, P. (2014). Impact of windows and daylight exposure on overall health and sleep quality of office workers: a case-control pilot study . Journal of Clinical Sleep Medicine : JCSM : Official Publication of the American Academy of Sleep Medicine, 10 (6), 603-611. https://doi.org/10.5664/jcsm.3780

This pilot study explored the impact of exposure to daylight on the health of office workers (measuring well-being and sleep quality subjectively, and light exposure, activity level and sleep-wake patterns via actigraphy). Individuals with windows in their workplaces had more light exposure, longer sleep duration, and more physical activity. They also reported a better scores in the areas of vitality and role limitations due to physical problems, better sleep quality and less sleep disturbances.

Togha, M., Razeghi Jahromi, S., Ghorbani, Z., Martami, F., & Seifishahpar, M. (2018). Serum Vitamin D Status in a Group of Migraine Patients Compared With Healthy Controls: A Case-Control Study . Headache, 58 (10), 1530-1540. https://doi.org/10.1111/head.13423

This case-control study compared serum vitamin D levels in individuals who experience migraine headaches with their matched controls. Studied over a period of thirty days, individuals with higher levels of serum Vitamin D was associated with lower odds of migraine headache.

Related Formulas

  • Odds ratio in an unmatched study
  • Odds ratio in a matched study

Related Terms

A patient with the disease or outcome of interest.

Confounding

When an exposure and an outcome are both strongly associated with a third variable.

A patient who does not have the disease or outcome.

Matched Design

Each case is matched individually with a control according to certain characteristics such as age and gender. It is important to remember that the concordant pairs (pairs in which the case and control are either both exposed or both not exposed) tell us nothing about the risk of exposure separately for cases or controls.

Observed Assignment

The method of assignment of individuals to study and control groups in observational studies when the investigator does not intervene to perform the assignment.

Unmatched Design

The controls are a sample from a suitable non-affected population.

Now test yourself!

1. Case Control Studies are prospective in that they follow the cases and controls over time and observe what occurs.

a) True b) False

2. Which of the following is an advantage of Case Control Studies?

a) They can simultaneously look at multiple risk factors. b) They are useful to initially establish an association between a risk factor and a disease or outcome. c) They take less time to complete because the condition or disease has already occurred. d) b and c only e) a, b, and c

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What Is A Case Control Study?

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Editor at Simply Psychology

BA (Hons) Psychology, Princeton University

Julia Simkus is a graduate of Princeton University with a Bachelor of Arts in Psychology. She is currently studying for a Master's Degree in Counseling for Mental Health and Wellness in September 2023. Julia's research has been published in peer reviewed journals.

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Olivia Guy-Evans is a writer and associate editor for Simply Psychology. She has previously worked in healthcare and educational sectors.

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A case-control study is a research method where two groups of people are compared – those with the condition (cases) and those without (controls). By looking at their past, researchers try to identify what factors might have contributed to the condition in the ‘case’ group.

Explanation

A case-control study looks at people who already have a certain condition (cases) and people who don’t (controls). By comparing these two groups, researchers try to figure out what might have caused the condition. They look into the past to find clues, like habits or experiences, that are different between the two groups.

The “cases” are the individuals with the disease or condition under study, and the “controls” are similar individuals without the disease or condition of interest.

The controls should have similar characteristics (i.e., age, sex, demographic, health status) to the cases to mitigate the effects of confounding variables .

Case-control studies identify any associations between an exposure and an outcome and help researchers form hypotheses about a particular population.

Researchers will first identify the two groups, and then look back in time to investigate which subjects in each group were exposed to the condition.

If the exposure is found more commonly in the cases than the controls, the researcher can hypothesize that the exposure may be linked to the outcome of interest.

Case Control Study

Figure: Schematic diagram of case-control study design. Kenneth F. Schulz and David A. Grimes (2002) Case-control studies: research in reverse . The Lancet Volume 359, Issue 9304, 431 – 434

Quick, inexpensive, and simple

Because these studies use already existing data and do not require any follow-up with subjects, they tend to be quicker and cheaper than other types of research. Case-control studies also do not require large sample sizes.

Beneficial for studying rare diseases

Researchers in case-control studies start with a population of people known to have the target disease instead of following a population and waiting to see who develops it. This enables researchers to identify current cases and enroll a sufficient number of patients with a particular rare disease.

Useful for preliminary research

Case-control studies are beneficial for an initial investigation of a suspected risk factor for a condition. The information obtained from cross-sectional studies then enables researchers to conduct further data analyses to explore any relationships in more depth.

Limitations

Subject to recall bias.

Participants might be unable to remember when they were exposed or omit other details that are important for the study. In addition, those with the outcome are more likely to recall and report exposures more clearly than those without the outcome.

Difficulty finding a suitable control group

It is important that the case group and the control group have almost the same characteristics, such as age, gender, demographics, and health status.

Forming an accurate control group can be challenging, so sometimes researchers enroll multiple control groups to bolster the strength of the case-control study.

Do not demonstrate causation

Case-control studies may prove an association between exposures and outcomes, but they can not demonstrate causation.

A case-control study is an observational study where researchers analyzed two groups of people (cases and controls) to look at factors associated with particular diseases or outcomes.

Below are some examples of case-control studies:
  • Investigating the impact of exposure to daylight on the health of office workers (Boubekri et al., 2014).
  • Comparing serum vitamin D levels in individuals who experience migraine headaches with their matched controls (Togha et al., 2018).
  • Analyzing correlations between parental smoking and childhood asthma (Strachan and Cook, 1998).
  • Studying the relationship between elevated concentrations of homocysteine and an increased risk of vascular diseases (Ford et al., 2002).
  • Assessing the magnitude of the association between Helicobacter pylori and the incidence of gastric cancer (Helicobacter and Cancer Collaborative Group, 2001).
  • Evaluating the association between breast cancer risk and saturated fat intake in postmenopausal women (Howe et al., 1990).

Frequently asked questions

1. what’s the difference between a case-control study and a cross-sectional study.

Case-control studies are different from cross-sectional studies in that case-control studies compare groups retrospectively while cross-sectional studies analyze information about a population at a specific point in time.

In  cross-sectional studies , researchers are simply examining a group of participants and depicting what already exists in the population.

2. What’s the difference between a case-control study and a longitudinal study?

Case-control studies compare groups retrospectively, while longitudinal studies can compare groups either retrospectively or prospectively.

In a  longitudinal study , researchers monitor a population over an extended period of time, and they can be used to study developmental shifts and understand how certain things change as we age.

In addition, case-control studies look at a single subject or a single case, whereas longitudinal studies can be conducted on a large group of subjects.

3. What’s the difference between a case-control study and a retrospective cohort study?

Case-control studies are retrospective as researchers begin with an outcome and trace backward to investigate exposure; however, they differ from retrospective cohort studies.

In a  retrospective cohort study , researchers examine a group before any of the subjects have developed the disease, then examine any factors that differed between the individuals who developed the condition and those who did not.

Thus, the outcome is measured after exposure in retrospective cohort studies, whereas the outcome is measured before the exposure in case-control studies.

Boubekri, M., Cheung, I., Reid, K., Wang, C., & Zee, P. (2014). Impact of windows and daylight exposure on overall health and sleep quality of office workers: a case-control pilot study. Journal of Clinical Sleep Medicine: JCSM: Official Publication of the American Academy of Sleep Medicine, 10 (6), 603-611.

Ford, E. S., Smith, S. J., Stroup, D. F., Steinberg, K. K., Mueller, P. W., & Thacker, S. B. (2002). Homocyst (e) ine and cardiovascular disease: a systematic review of the evidence with special emphasis on case-control studies and nested case-control studies. International journal of epidemiology, 31 (1), 59-70.

Helicobacter and Cancer Collaborative Group. (2001). Gastric cancer and Helicobacter pylori: a combined analysis of 12 case control studies nested within prospective cohorts. Gut, 49 (3), 347-353.

Howe, G. R., Hirohata, T., Hislop, T. G., Iscovich, J. M., Yuan, J. M., Katsouyanni, K., … & Shunzhang, Y. (1990). Dietary factors and risk of breast cancer: combined analysis of 12 case—control studies. JNCI: Journal of the National Cancer Institute, 82 (7), 561-569.

Lewallen, S., & Courtright, P. (1998). Epidemiology in practice: case-control studies. Community eye health, 11 (28), 57–58.

Strachan, D. P., & Cook, D. G. (1998). Parental smoking and childhood asthma: longitudinal and case-control studies. Thorax, 53 (3), 204-212.

Tenny, S., Kerndt, C. C., & Hoffman, M. R. (2021). Case Control Studies. In StatPearls . StatPearls Publishing.

Togha, M., Razeghi Jahromi, S., Ghorbani, Z., Martami, F., & Seifishahpar, M. (2018). Serum Vitamin D Status in a Group of Migraine Patients Compared With Healthy Controls: A Case-Control Study. Headache, 58 (10), 1530-1540.

Further Information

  • Schulz, K. F., & Grimes, D. A. (2002). Case-control studies: research in reverse. The Lancet, 359(9304), 431-434.
  • What is a case-control study?

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The First-Ever Investigation of SNP rs119461977 in SECISBP2/SBP2 Gene and its Implications for Hypothyroidism: A Novel Case–Control Research

  • ORIGINAL RESEARCH ARTICLE
  • Published: 20 February 2024

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  • Manpreet Kaur 1 ,
  • Shama Tyagi 1 ,
  • Anita Yadav 2 &
  • Ranjan Gupta 1  

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Hypothyroidism is one of the most prevalent endocrine disorders worldwide. Various genes are involved in thyroid hormone production, regulation, and metabolism. SBP2 is required for the adequate assembly of selenoproteins, which are further required for thyroid hormone metabolism. Present case–control study aims to investigate the association of the K438X (rs119461977) variant situated on exon 10 of the gene with biochemical parameters and hypothyroidism. Our study comprises 253 subjects, 136 healthy control (Female 70, Male 66), and 117 case hypothyroid patients (Female 81, Male 36). Biochemical parameters were estimated using an automatic analyzer. PCR-RFLP method was used for genotyping. Heterozygous and homozygous mutant genotypes are higher among the cases as compared to control and shows significant association ( p —0.0004). The frequency of minor alleles is significantly higher in cases than in control ( p —0.0018). The dominant genetic model shows a two-fold disease risk (χ 2 —6.8505, OR—2.019, 95%CI 2.2779–1.74118, p value—0.008). Recessive and additive models also suggest a significant association with hypothyroidism ( p —0.0005, 0.00066). This study indicates the novel association of rs119461977 of the SBP2 gene with hypothyroidism. This association underlines the importance of selenoproteins synthesis in the pathogenesis of hypothyroidism.

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Author thanks all the participants involved in this study for providing their consents.

This study was funded by Department of Science and Technology, Haryana as JRF, Haryana State Council for Science Innovation and Technology (HSCSIT).

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Kaur, M., Tyagi, S., Yadav, A. et al. The First-Ever Investigation of SNP rs119461977 in SECISBP2/SBP2 Gene and its Implications for Hypothyroidism: A Novel Case–Control Research. Ind J Clin Biochem (2024). https://doi.org/10.1007/s12291-024-01192-1

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Epidemiology in Practice: Case-Control Studies

Introduction.

A case-control study is designed to help determine if an exposure is associated with an outcome (i.e., disease or condition of interest). In theory, the case-control study can be described simply. First, identify the cases (a group known to have the outcome) and the controls (a group known to be free of the outcome). Then, look back in time to learn which subjects in each group had the exposure(s), comparing the frequency of the exposure in the case group to the control group.

By definition, a case-control study is always retrospective because it starts with an outcome then traces back to investigate exposures. When the subjects are enrolled in their respective groups, the outcome of each subject is already known by the investigator. This, and not the fact that the investigator usually makes use of previously collected data, is what makes case-control studies ‘retrospective’.

Advantages of Case-Control Studies

Case-control studies have specific advantages compared to other study designs. They are comparatively quick, inexpensive, and easy. They are particularly appropriate for (1) investigating outbreaks, and (2) studying rare diseases or outcomes. An example of (1) would be a study of endophthalmitis following ocular surgery. When an outbreak is in progress, answers must be obtained quickly. An example of (2) would be a study of risk factors for uveal melanoma, or corneal ulcers. Since case-control studies start with people known to have the outcome (rather than starting with a population free of disease and waiting to see who develops it) it is possible to enroll a sufficient number of patients with a rare disease. The practical value of producing rapid results or investigating rare outcomes may outweigh the limitations of case-control studies. Because of their efficiency, they may also be ideal for preliminary investigation of a suspected risk factor for a common condition; conclusions may be used to justify a more costly and time-consuming longitudinal study later.

Consider a situation in which a large number of cases of post-operative endophthalmitis have occurred in a few weeks. The case group would consist of all those patients at the hospital who developed post-operative endophthalmitis during a pre-defined period.

The definition of a case needs to be very specific:

  • Within what period of time after operation will the development of endophthalmitis qualify as a case – one day, one week, or one month?
  • Will endophthalmitis have to be proven microbiologically, or will a clinical diagnosis be acceptable?
  • Clinical criteria must be identified in great detail. If microbiologic facilities are available, how will patients who have negative cultures be classified?
  • How will sterile inflammation be differentiated from endophthalmitis?

There are not necessarily any ‘right’ answers to these questions but they must be answered before the study begins. At the end of the study, the conclusions will be valid only for patients who have the same sort of ‘endophthalmitis’ as in the case definition.

Controls should be chosen who are similar in many ways to the cases. The factors (e.g., age, sex, time of hospitalisation) chosen to define how controls are to be similar to the cases are the ‘matching criteria’. The selected control group must be at similar risk of developing the outcome; it would not be appropriate to compare a group of controls who had traumatic corneal lacerations with cases who underwent elective intraocular surgery. In our example, controls could be defined as patients who underwent elective intraocular surgery during the same period of time.

Matching Cases and Controls

Although controls must be like the cases in many ways, it is possible to over-match. Over-matching can make it difficult to find enough controls. Also, once a matching variable has been selected, it is not possible to analyse it as a risk factor. Matching for type of intraocular surgery (e.g., secondary IOL implantation) would mean including the same percentage of controls as cases who had surgery to implant a secondary IOL; if this were done, it would not be possible to analyse secondary IOL implantation as a potential risk factor for endophthalmitis.

An important technique for adding power to a study is to enroll more than one control for every case. For statistical reasons, however, there is little gained by including more than two controls per case.

Collecting Data

After clearly defining cases and controls, decide on data to be collected; the same data must be collected in the same way from both groups. Care must be taken to be objective in the search for past risk factors, especially since the outcome is already known, or the study may suffer from researcher bias. Although it may not always be possible, it is important to try to mask the outcome from the person who is collecting risk factor information or interviewing patients. Sometimes it will be necessary to interview patients about potential factors (such as history of smoking, diet, use of traditional eye medicines, etc.) in their past. It may be difficult for some people to recall all these details accurately. Furthermore, patients who have the outcome (cases) are likely to scrutinize the past, remembering details of negative exposures more clearly than controls. This is known as recall bias. Anything the researcher can do to minimize this type of bias will strengthen the study.

Analysis; Odds Ratios and Confidence Intervals

In the analysis stage, calculate the frequency of each of the measured variables in each of the two groups. As a measure of the strength of the association between an exposure and the outcome, case-control studies yield the odds ratio. An odds ratio is the ratio of the odds of an exposure in the case group to the odds of an exposure in the control group. It is important to calculate a confidence interval for each odds ratio. A confidence interval that includes 1.0 means that the association between the exposure and outcome could have been found by chance alone and that the association is not statistically significant. An odds ratio without a confidence interval is not very meaningful. These calculations are usually made with computer programmes (e.g., Epi-Info). Case-control studies cannot provide any information about the incidence or prevalence of a disease because no measurements are made in a population based sample.

Risk Factors and Sampling

Another use for case-control studies is investigating risk factors for a rare disease, such as uveal melanoma. In this example, cases might be recruited by using hospital records. Patients who present to hospital, however, may not be representative of the population who get melanoma. If, for example, women present less commonly at hospital, bias might occur in the selection of cases.

The selection of a proper control group may pose problems. A frequent source of controls is patients from the same hospital who do not have the outcome. However, hospitalised patients often do not represent the general population; they are likely to suffer health problems and they have access to the health care system. An alternative may be to enroll community controls, people from the same neighborhoods as the cases. Care must be taken with sampling to ensure that the controls represent a ‘normal’ risk profile. Sometimes researchers enroll multiple control groups . These could include a set of community controls and a set of hospital controls.

Confounders

Matching controls to cases will mitigate the effects of confounders . A confounding variable is one which is associated with the exposure and is a cause of the outcome. If exposure to toxin ‘X’ is associated with melanoma, but exposure to toxin ‘X’ is also associated with exposure to sunlight (assuming that sunlight is a risk factor for melanoma), then sunlight is a potential confounder of the association between toxin ‘X’ and melanoma.

Case-control studies may prove an association but they do not demonstrate causation. Consider a case-control study intended to establish an association between the use of traditional eye medicines (TEM) and corneal ulcers. TEM might cause corneal ulcers but it is also possible that the presence of a corneal ulcer leads some people to use TEM. The temporal relationship between the supposed cause and effect cannot be determined by a case-control study.

Be aware that the term ‘case-control study’ is frequently misused. All studies which contain ‘cases’ and ‘controls’ are not case-control studies. One may start with a group of people with a known exposure and a comparison group (‘control group’) without the exposure and follow them through time to see what outcomes result, but this does not constitute a case-control study.

Case-control studies are sometimes less valued for being retrospective. However, they can be a very efficient way of identifying an association between an exposure and an outcome. Sometimes they are the only ethical way to investigate an association. If care is taken with definitions, selection of controls, and reducing the potential for bias, case-control studies can generate valuable information.

Case-Control Studies: Advantages and Disadvantages

Recommended Reading

  • Open access
  • Published: 17 February 2024

The body mass index and the risk of ectopic pregnancy: a 5-year retrospective case-control study

  • Jin-Shuang Ji 1 ,
  • Ling Liu 2 ,
  • Huan Huang 1 ,
  • Hong-Wei Chen 1 ,
  • Li Xiao 1 , 2 ,
  • Xiang-Yi Lu 1 ,
  • Yang-Yang Ni 1 ,
  • Wen-Juan Jia 1 &
  • Lei Huang 1 , 2  

BMC Pregnancy and Childbirth volume  24 , Article number:  143 ( 2024 ) Cite this article

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Metrics details

Acknowledging the associated risk factors may have a positive impact on reducing the incidence of ectopic pregnancy (EP). In recent years, body mass index (BMI) has been mentioned in research. However, few studies are available and controversial on the relationship between EP and BMI.

We retrospectively studied the EP women as a case group and the deliveries as a control group in the central hospital of Wuhan during 2017 ~ 2021. χ 2 test of variables associated with ectopic pregnancy was performed to find differences. Univariate and multivariate binary logistic regression analysis was conducted to analyze the association of the variables of age, parity, history of induced abortion, history of ectopic pregnancy, history of spontaneous abortion, history of appendectomy surgery and BMI (< 18.5 kg/m 2 , 18.5 ~ 24.9 kg/m 2 , 25 kg/m 2  ~ 29.9 kg/m 2 , ≥ 30 kg /m 2 ) with EP.

They were 659 EP and 1460 deliveries. The variables of age, parity, history of induced abortion, history of ectopic pregnancy and BMI were different significantly( P  < 0.05). Multivariate analysis showed that the variables of age > 35 years old [(OR (Odds Ratio), 5.415; 95%CI (Confidence Interval), 4.006 ~ 7.320, P  < 0.001], history of ectopic pregnancy (OR, 3.944; 95%CI, 2.405 ~ 6.467; P  < 0.001), history of induced abortion(OR, 3.365; 95%CI, 2.724 ~ 4.158, P  < 0.001) and low BMI (< 18.5 kg/m 2 ) (OR, 1.929; 95%CI, 1.416 ~ 2.628, P  < 0.001])increased the risk of EP.

The history of ectopic pregnancy, history of induced abortion and age > 35 years old were the risk factors with EP. In addition to these traditional factors, we found low BMI (< 18.5 kg/m 2 ) with women may increase the risk to EP.

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Introduction

Ectopic pregnancy (EP) refers to a pregnancy that occurs outside the uterine cavity, and the incidence rate accounts for about 1%~2% of all pregnancies [ 1 , 2 ]. More than 90% of EP are tubal pregnancy accounting for the first maternal mortality rate in first-trimester pregnancy [ 3 , 4 ]. Nowadays, the incidence of ectopic pregnancy is still on the rise worldwide [ 5 , 6 , 7 ]. We have known that the risk factors for EP, including the history of ectopic pregnancy, the history of tubal surgery, the history of induced abortion, the history of spontaneous abortion, chlamydial infection and pelvic inflammatory disease, the history of infertility, the history of smoking, age > 35 years old [ 8 , 9 , 10 , 11 , 12 ]. With the growth of economic level and the improvement of people’s living standard, risk factors for ectopic pregnancy are also in change.

In recent years, due to aesthetic aberrations, more and more women pursued the ideal body or were underweight [ 13 , 14 ]. And in clinical workflow, we observed patients with ectopic pregnancies were lean. Whether there is some association between body mass index (BMI) and ectopic pregnancy. In a prospective study, it suggested that low BMI was associated with EP after receiving assisted reproductive technology (ART) [ 15 ]. Another study suggested that obese women were at higher risk of ectopic pregnancy [ 16 ]. However, BMI may not be associated with ectopic pregnancy in other studies [ 11 , 17 ]. At present, there are different opinions on the relationship between BMI and EP. The findings of these studies are conflicting, and the studies on BMI did not control other related risk factors. So, there is some bias. There are few studies on the direct relationship between BMI and EP, and further research is needed to confirm their relationship.

This study was retrospective case-control research in the central hospital of Wuhan during 2017 ~ 2021. We included BMI in the study of risk factors. We performed univariate and multivariate binary logistic regression analysis to find relationship between BMI and EP. We found a new risk factor for ectopic pregnancy. It alerts and advocates women to have a healthy body mass index to protect fertility.

Study population

We retrospectively studied the case of ectopic pregnancy (EP) as a case group in the central hospital of Wuhan during 2017 ~ 2021. And pregnant women who gave birth and filed in this hospital during the same period were randomly selected as the control group (according to the order of registration, 10 records were randomly selected from each page). Prepregnancy height (m), weight (kg) and other mask data were provided by the medical information department of the hospital and filing system. This study had been approved by the institutional ethics committees of the central hospital of Wuhan.

Diagnosis of ectopic pregnancy: confirmed by laparoscopic surgery and pathological diagnosis. A retrospective cohort study was conducted in the central hospital of Wuhan between January 2017 and December 2021. Inclusion criteria: Women aged 18–45 years, Cases with height and weight information. Exclusion criteria: The history of assisted reproductive technology (ART), those with metabolic diseases such as hypertension, diabetes, heart disease, polycystic ovary syndrome (PCOS), hyperthyroidism and hypothyroidism, and malignant tumors, because of missing data. According to the inclusion and exclusion criteria, the case group and control group were obtained. The flowchart of the study was in (Fig.  1 ).

Study variables

Sociodemographic characteristics, including age, occupation and region. For comparability between ectopic pregnancy and delivery, we included the previously known risk factors of EP, these variables were age, parity, history of induced abortion, history of ectopic pregnancy, history of spontaneous abortion, history of appendectomy surgery and BMI. According to the World Health Organization (WHO) of classification standard of BMI in 2021, it is divided into low BMI (< 18.5 kg/m 2 ), normal BMI (18.5 ~ 24.9 kg/m 2 ), overweight (25 ~ 29.9 kg/m 2 ), obesity (≥ 30 kg /m 2 ). BMI is defined as the body weight divided by the square of height.

Study outcomes

The primary outcomes of this study were age > 35 years old, history of induced abortion, history of ectopic pregnancy, low BMI (< 18.5 kg/m 2 ).

Statistical analysis

Categorical variables were expressed as frequencies and percentages, and χ 2 test was used to assess the difference of variables. Binomial logistic regression was for univariate and multivariate analyses.

IBM SPSS Statistics (R26.0.0.0) software was used for data analysis and GraphPad prism (R9.3.1) software for graphing. All comparisons were two-tailed. When P value < 0.05, the results were considered statistically significant.

figure 1

The flowchart of the study

Sociodemographic characteristics of women

The sociodemographic characteristics of age, region and occupation in the 2119 women were in Table  1 . The results showed that there were 659 EP in the case group and 1460 deliveries in the control group. There were significant differences in age and occupation between groups ( P  < 0.001). The median age of EP patients were 31(27 ~ 36) years old. In these women, 949 (46.2%) women were employees, and 272 (42.2%) patients with EP were employees. region distribution showed no significant differences between groups ( P  = 0.418).

Analysis for the clinical characteristics of ectopic pregnancy

We included risk factors associated with ectopic pregnancy, then performed chi-square test to compare these variables. The results showed that history of spontaneous abortion and history of appendectomy surgery was not statistically significant( P  > 0.05). However, the variables of age, parity, history of induced abortion, History of ectopic pregnancy and BMI were different significantly( P  < 0.001). 498(75.6%) patients with EP were normal BMI. 89(13.5%) EP was low BMI. 59(9.0%) patients with EP were overweight. 13(2.0%) EP was obesity. In summary, the majority of patients (75.6%) of EP was normal BMI, secondly 13.5% patients with EP were low BMI (Table  2 ).

Univariate and multivariate analysis of risk factors of ectopic pregnancy

We performed univariate and multivariate binomial logistic regression analysis to find risk factors of EP. univariate analysis showed that the variables of age, parity, history of induced abortion, history of ectopic pregnancy and BMI were risk factors of EP ( P  < 0.001). The history of spontaneous abortion was the risk factor with EP and but not statistically significant ( P  = 0.176). the history of appendectomy surgery was the protective factor with EP and but not statistically significant ( P  = 0.569).

Multivariate analysis revealed that the variables of age, history of induced abortion, history of ectopic pregnancy and BMI were risk factors for EP( P  < 0.001). according to the value of Odds Ratio from large to small size was age > 35 years old [OR, 5.415; 95%CI, 4.006 ~ 7.320, P  < 0.001], history of ectopic pregnancy [OR, 3.944; 95%CI, 2.405 ~ 6.467; P  < 0.001], history of induced abortion[(OR, 3.365; 95%CI, 2.724 ~ 4.158, P  < 0.001], low BMI (< 18.5 kg/m 2 ) [(OR, 1.929; 95%CI, 1.416 ~ 2.628, P  < 0.001].And yet, Overweight (25 kg/m 2  ~ 29.9 kg/m 2 ) was the risk factor of EP but no statistically significant ( P  = 0.331), obesity(≥ 30 kg/m 2 ) was the protective factor with EP insignificantly ( P  = 0.803) (Fig.  2 ).

figure 2

Forest plot of univariate and multivariate of binomial logical regression analysis of EP

In this study, we directly included risk factors associated with ectopic pregnancy as well as body mass index to conduct univariate and multivariate analysis. This is a relatively systematic study of risk factors for ectopic pregnancy, a new variable of body mass index was also included. We found the history of ectopic pregnancy, history of induced abortion, age > 35 years old and low BMI (< 18.5 kg/m 2 ) were the risk factors with EP. And low BMI (< 18.5 kg/m 2 ) was 1.929 times higher risk to EP compared with normal BMI (18.5 kg/m 2  ~ 24.9 kg/m 2 ). Our findings hope that it may improve awareness of these factors, and further research common to these conditions.

Theoretically, any condition that prevents or retards migration of the fertilized ovum to the uterus could predispose a woman to ectopic gestation (current intrauterine device use, the history of infertility, the history of pelvic inflammatory disease, and prior tubal surgery) [ 18 ]. As the economy develops, more and more women choose the contraceptive method of IUD. The risk of ectopic pregnancy in different types of intrauterine device may be different, and the concentration of drugs in IUDs may have some mechanism of action with fallopian tube function. In addition, IUDs are foreign to the uterine cavity and may cause the endometrium to be out of sync with fallopian tube function [ 19 , 20 ]. Pelvic inflammatory disease (PID) changes the inner environment of the pelvic uterus, affecting the transport environment of fallopian tubes, thereby increasing the risk of ectopic pregnancy. The two most common pathogens, Neisseria gonorrhoea and chlamydia trachomatis, have been shown to be mainly associated with ectopic pregnancy [ 21 , 22 , 23 ]. Whether the inflammation caused by appendicitis also affects the function of fallopian tubes, there is currently no evidence of higher levels. However, some retrospective studies have shown that the history of appendectomy is associated with increasing risk of ectopic pregnancy [ 24 ]. In contrast to our study, we found that women with previous history of appendectomy were not at increased risk of ectopic pregnancy, either through univariate analysis or and multivariate analysis. So, the problem is whether abdominal surgery or inflammation of the appendix caused the ectopic pregnancy. Similarly, the history of two or three cesarean deliveries is associated with increased risk for subsequent ectopic pregnancy in relation to women who had one prior cesarean delivery [ 25 ]. We hypothesize that multiple prior cesareans may increase pelvic adhesion leading to tubal hypoplasia. However, there is no experimental evidence.

With age, some risk factors associated with ectopic pregnancy may accumulate. Epidemiological surveys showed a worldwide phenomenon of postponement of the age of childbearing to the 30s, fertility rates were also declining [ 26 ]. With the improvement of economic and educational level, the divorce rate and multiple sexual partners among these women are likely to increase [ 27 ]. This may lead to pelvic inflammatory disease and tubal disease, and ectopic pregnancy. In a Chinese study, the proportion of EP among those ≥ 35 years old was reversed from a downward trend (2011–2016 annual percentage change (APC) − 4.13) to an upward trend (2016–2020 APC 4.04) [ 28 ]. Some study showed that age > 35 years increased the risk of ectopic pregnancy [ 29 , 30 ]. In agreement with our data, ectopic pregnancy was more likely to occur over the age of 35, the value of odds ratio was 5.415 and the largest in this study, there was a major impact effect on ectopic pregnancy.

There has been a great deal of research showing that an increased risk of repeat EP in patients with history of ectopic pregnancies. In a large French case-control study, women with one ectopic pregnancy had the higher risk of repeated ectopic pregnancy (OR = 12.5), especially for women with two or more ectopic pregnancies [ 9 ]. In a recent study, women with the history of ectopic pregnancy had the 2.72 times higher risk of ectopic pregnancy recurrence (Adjusted odds ratio [AOR] = 2.72, 95% confidence interval [CI]: 1.83–4.05) [ 19 ]. In our study, multivariate analysis showed that the risk of ectopic pregnancy was 3.944 times higher in women with the history of ectopic pregnancy. Women with previous history of ectopic pregnancy may affect fallopian tube function after conservative or surgical treatment, such as oviduct blockage, oviduct water accumulation, oviduct inflammation, etc.

Induced abortion remains noticeable in China [ 31 ]. In a recent cross-sectional study, of all abortions, 65.2% were repeat induced abortions [ 32 ]. The history of induced abortion was associated with an increased risk of ectopic pregnancy [OR, 1.5; 95%CI, 1.0 ~ 2.0], particularly in the case of women who have had several induced abortions [ 33 ]. In a prospective study by Skjeldestad, Induced abortion did not increase the risk of ectopic pregnancy [ 34 ]. In our study, the history of induced abortion was significantly associated with ectopic pregnancy(OR, 3.365; 95%CI, 2.724 ~ 4.158). But the relationship between history of spontaneous abortion and ectopic pregnancy was no statistically significant. We assumed that one or more abortions increased the chance of uterine manipulation, leading to an enhanced risk of uterine infection. The possibility of pelvic inflammatory disease and tubal disease cannot be excluded.

In this study, we considered the inclusion of body mass index to explore the risk factors for ectopic pregnancy. However, the relationship between BMI and EP is rarely studied. Pan pointed out that obese women have a higher risk of EP [ 16 ], and it was suggested that low BMI was associated with EP after receiving ART in this prospective study [ 15 ]. In these studies, the relationship between BMI and EP was not directly investigated, and other factors associated with EP were not controlled. Therefore, there was difference. In our study, by including risk factors associated with EP, multivariate analysis showed that body mass index was associated with EP after adjustment and appeared in low BMI (< 18.5 kg/m 2 ). There were few reports in the literature on the mechanism. We consider that leptin levels in women with low body mass index are alternately regulated with insulin growth factor-1 [ 35 , 36 ], and that leptin is critically linked to reproductive function [ 37 ]. However, a unique hormonal regulation exists during embryonic development, maturation, and egg transport through the fallopian oviduct [ 38 ]. This suggests that it may affect embryonic development and fallopian tube function by impacting hormonal regulation.

This study is a retrospective study, which effect is less than randomized controlled studies. Subsequent multicenter trial and large-sample research is required. The BMI is a new risk factor compared to other factors, which is a highlight of our research. We are better able to regulate weight relative to other physiological factors to guide the clinical.

The history of ectopic pregnancy, history of induced abortion and age > 35 years old were the risk factors with EP. In addition to the traditional risk factors, we found an association between body mass index and the risk of ectopic pregnancy. Women with a low BMI (< 18.5 kg/m 2 ) had a slightly higher risk of ectopic pregnancy than women with normal BMI. We hope future studies focus on these risk factors and advocate a healthy body mass index to protect female fertility by improving body mass index.

Data availability

The datasets used and/or analyzed during the current study are available from the corresponding author on reasonable request.

Abbreviations

Ectopic pregnancy

Body mass index

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Acknowledgements

I would like to express my gratitude to Prof. Xiong Li and Prof. Jin-Ming Fang for their great support and help on my project. They gave me so much constructive help for statistical analysis.

This work was supported by Project Health Commission of Hubei Province (WJ2021D006) , Project Health Commission of Wuhan City (WX20A05) and Electrophysiological Foundation of Chinese Association of Plastics and Aesthetics [2022]02015.

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Department of Gynecology & Obstetrics, Tongji Medical College, The Central Hospital of Wuhan, Huazhong University of Science and Technology, Wuhan, 430014, Hubei, China

Jin-Shuang Ji, Huan Huang, Hong-Wei Chen, Li Xiao, Xiang-Yi Lu, Yang-Yang Ni, Wen-Juan Jia & Lei Huang

The Diagnosis and Therapy Center of Pelvic Floor Rehabilitation and Electrophysiology, Tongji Medical College, The Central Hospital of Wuhan, Huazhong University of Science and Technology, Wuhan, 430014, Hubei, China

Ling Liu, Li Xiao & Lei Huang

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All authors contributed to the study conception and design. Material preparation, data collection and analysis were performed by Jin-Shuang Ji, Ling Liu, Huan Huang, Hong-Wei Chen, Li Xiao, Xiang-Yi Lu, Yang-Yang Ni, Wen-Juan Jia, Lei Huang. The first draft of the manuscript was written by Jin-Shuang Ji and all authors commented on previous versions of the manuscript. All authors read and approved the final manuscript.

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Research has been performed in accordance with the Declaration of Helsinki. The study was approved by the Ethics Committee of The Central Hospital of Wuhan, Affiliated Hospital of Huazhong University of Science and Technology (No. 2022WHZXKYL034). As this study is a retrospective study, it will not adversely affect the health of patients, nor will it involve the privacy and personal identity information of patients. The Ethics Committee of The Central Hospital of Wuhan, Affiliated with Hospital of Huazhong University of Science and Technology has waived the requirement of informed consent of patients.

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Ji, JS., Liu, L., Huang, H. et al. The body mass index and the risk of ectopic pregnancy: a 5-year retrospective case-control study. BMC Pregnancy Childbirth 24 , 143 (2024). https://doi.org/10.1186/s12884-024-06319-z

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DOI : https://doi.org/10.1186/s12884-024-06319-z

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case control studies in research

Influence of quality of life related to perceived foot health between in a rural an urban population: A case-control research

Affiliations.

  • 1 Research, Health, and Podiatry Group, Department of Health Sciences, Faculty of Nursing and Podiatry, Industrial Campus of Ferrol, Universidade da Coruña, Ferrol, Spain.
  • 2 Faculty of Nursing and Podiatry, Department of Nursing, University of Valencia, Frailty Research Organizaded Group (FROG), Valencia, Spain.
  • 3 Faculty of Health Sciences, Universidad Rey Juan Carlos, Alcorcon, Spain.
  • 4 Faculty of Nursing, Physiotherapy and Podiatry, Universidad Complutense de Madrid, Madrid, Spain.
  • 5 Group of Research in Sport Science (INCIDE), Department of Physical Education and Sport, Universidade da Coruña, A Coruña, Spain.
  • 6 Department of Sociology, Social Work and Public Health, Faculty of Labour Sciences, University of Huelva, Huelva, Spain.
  • 7 Safety and Health Postgraduate Programme, Universidad Espíritu Santo, Guayaquil, Ecuador.
  • PMID: 38356326
  • PMCID: PMC10867538
  • DOI: 10.1111/iwj.14713

Foot problems are very common in the community. Studies indicate that between 18% and 63% of people have foot pain or stiffness and that foot problems have a large impact on people's functional decline and a significant detrimental impact on measures of quality of life related to health. The general objective of this research was to compare foot health in people from the rural population compared to people from the urban population and its relationship with quality of life. A case-control descriptive study was developed with a sample of 304 patients, 152 patients from the rural population and 152 patients from the urban population. Quality of life was measured through the SF-36 Health Questionnaire in its Spanish version. The rural population group had a mean age of 46.67 ± 13.69 and the urban population group 49.02 ± 18.29. Regarding the score of the lowest levels of quality of life related to foot problems, the rural population group compared to the urban population group showed: for body pain (52.21 ± 30.71 vs. 67.80 ± 25.28, p < 0.001); and for mental health (69.58 ± 18.98 vs. 64.60 ± 14.88, p < 0.006). Differences between groups were analysed using Student's t-test for independent samples, which showed statistical significance (p < 0.05). This research offers evidence that the rural population presents better levels of mental health and lower levels of bodily pain in the domains of the SF-36 Health Questionnaire comparing with the urban population.

Keywords: foot diseases; psychological well-being; quality of life; rural health; urban health.

© 2024 The Authors. International Wound Journal published by Medicalhelplines.com Inc and John Wiley & Sons Ltd.

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  1. What Is a Case-Control Study?

    Case-control studies are a type of observational study often used in fields like medical research, environmental health, or epidemiology. While most observational studies are qualitative in nature, case-control studies can also be quantitative, and they often are in healthcare settings.

  2. Case Control Studies

    A case-control study is a type of observational study commonly used to look at factors associated with diseases or outcomes. [1] The case-control study starts with a group of cases, which are the individuals who have the outcome of interest.

  3. A Practical Overview of Case-Control Studies in Clinical Practice

    In a case-control study the researcher identifies a case group and a control group, with and without the outcome of interest. Such a study design is called observational because the researcher does not control the assignment of a subject to one of the groups, unlike in a planned experimental study.

  4. Research Design: Case-Control Studies

    Case-control studies are observational studies in which cases are subjects who have a characteristic of interest, such as a clinical diagnosis, and controls are (usually) matched subjects who do not have that characteristic.

  5. Case Control Studies

    Treasure Island (FL): StatPearls Publishing; 2024 Jan. Excerpt A case-control study is a type of observational study commonly used to look at factors associated with diseases or outcomes. The case-control study starts with a group of cases, which are the individuals who have the outcome of interest.

  6. Case-control study

    A case-control study (also known as case-referent study) is a type of observational study in which two existing groups differing in outcome are identified and compared on the basis of some supposed causal attribute.

  7. A Practical Overview of Case-Control Studies in Clinical Practice

    Case-control studies are one of the major observational study designs for performing clinical research. The advantages of these study designs over other study designs are that they are relatively quick to perform, economical, and easy to design and implement.

  8. Case Control Study: Definition, Benefits & Examples

    Case-control studies are observational studies because researchers do not control the risk factors—they only observe them. They are retrospective studies because the scientists create the case and control groups after the outcomes for the subjects (e.g., disease vs. no disease) are known.

  9. Design and data analysis case-controlled study in clinical research

    Case-control studies are one of the most frequently used study designs for these purposes. This paper explains basic features of case control studies, rationality behind applying case control design with appropriate examples and limitations of this design.

  10. PDF Case-control studies: an efficient study design

    Case-control studies are particularly useful for studying ... Case-control studies: research in reverse. Lancet. 2002;359:431-4. 10. Pearl J, McKenzie D. The Book of Why. The New Science of

  11. Case-control study in medical research: Uses and limitations

    A case-control study is a type of medical research investigation often used to help determine the cause of a disease, particularly when investigating a disease outbreak or rare condition.

  12. Case Control

    Case control studies are observational because no intervention is attempted and no attempt is made to alter the course of the disease. The goal is to retrospectively determine the exposure to the risk factor of interest from each of the two groups of individuals: cases and controls. These studies are designed to estimate odds.

  13. Case Control Study: Definition & Examples

    A case-control study is a research method where two groups of people are compared - those with the condition (cases) and those without (controls). By looking at their past, researchers try to identify what factors might have contributed to the condition in the 'case' group. Definition

  14. Case-control studies: research in reverse

    Case-control studies contribute greatly to the research toolbox of an epidemiologist. They embody the strengths and weaknesses of observational epidemiology. Moreover, epidemiologists use them to study a huge variety of associations. To show this variety, we searched PubMed for topics investigated with case-control studies ( panel 1 ). 1 , 2 , 3 ,

  15. PDF Case-control studies: research in reverse

    Researchers would have to examine many cases and controls to find one who had been exposed. For instance, a case-control study of oral contraceptive use and transmission of HIV-1 would be impractical in parts of Africa because of the rarity of use of oral contraceptives.

  16. Research Design: Case-Control Studies

    Case-control studies are observational studies in which cases are subjects who have a characteristic of interest, such as a clinical diagnosis, and controls are (usually) matched subjects who do not have that characteristic.

  17. Case-control studies in clinical research: mechanism and ...

    DOI: 10.1006/pmed.1997.0189. The mechanism by which selection bias occurs in case-control studies is explained to an audience of clinicians using a simple conceptual framework and a graphical presentation. A case-control study consists in comparing the frequency of exposure in a group of subjects having the studied disease (the cases) relative ...

  18. Methodology Series Module 2: Case-control Studies

    Case-Control study design is a type of observational study. In this design, participants are selected for the study based on their outcome status. Thus, some participants have the outcome of interest (referred to as cases), whereas others do not have the outcome of interest (referred to as controls).

  19. Evaluation of the hematological inflammatory parameters in the patients

    For instance, study conducted by Ahmed et al. shown that a low lymphocyte count at the time of diagnosis was a prognostic factor for persistence in children with ITP. 27 Similarly, Deel et al. discovered that development of chronic ITP was associated with a low WBC count in the third month of the illness. 28 On the other hand, other research ...

  20. The First-Ever Investigation of SNP rs119461977 in SECISBP2 ...

    Hypothyroidism is one of the most prevalent endocrine disorders worldwide. Various genes are involved in thyroid hormone production, regulation, and metabolism. SBP2 is required for the adequate assembly of selenoproteins, which are further required for thyroid hormone metabolism. Present case-control study aims to investigate the association of the K438X (rs119461977) variant situated on ...

  21. Cochlear-facial dehiscence

    Retrospective case-control study of 27 patients with CI and FNS on either ear (study group) and 27 patients without FNS, matched for age, sex and type of electrode array (control group). ... Further research may prove whether intraoperative E-ABR can predict the risk of FNS, and whether it may be useful tool to facilitate a proper choice of ...

  22. Research Design: Case-Control Studies

    How do case-control studies fit into classifications of research design described in an earlier article? 1 Case-control studies are empirical studies that are based on samples, not individual cases or case series. They are cross-sectional because cases and controls are identified and evaluated for caseness, historical exposures, and confounding ...

  23. Epidemiology in Practice: Case-Control Studies

    Introduction. A case-control study is designed to help determine if an exposure is associated with an outcome (i.e., disease or condition of interest). In theory, the case-control study can be described simply. First, identify the cases (a group known to have the outcome) and the controls (a group known to be free of the outcome).

  24. Case-control studies: research in reverse

    The strength of case-control studies can be appreciated in early research done by investigators hoping to understand the cause of AIDS. Case-control studies identified risk groups—eg, homosexual men, intravenous drug users, and blood-transfusion recipients—and risk factors—eg, multiple sex partners, receptive anal intercourse in homosexual men, and not using condoms—for AIDS.

  25. The body mass index and the risk of ectopic pregnancy: a 5-year

    Purpose Acknowledging the associated risk factors may have a positive impact on reducing the incidence of ectopic pregnancy (EP). In recent years, body mass index (BMI) has been mentioned in research. However, few studies are available and controversial on the relationship between EP and BMI. Methods We retrospectively studied the EP women as a case group and the deliveries as a control group ...

  26. Influence of quality of life related to perceived foot health ...

    The general objective of this research was to compare foot health in people from the rural population compared to people from the urban population and its relationship with quality of life. A case-control descriptive study was developed with a sample of 304 patients, 152 patients from the rural population and 152 patients from the urban population.

  27. Assessing the excess costs of the in-hospital adverse events ...

    The Patient Safety Indicators (PSI) developed by the Agency for Healthcare Research and Quality aid healthcare organizations to identify potentially harmful events that compromise patient safety. This study from Switzerland shows the financial implications of PSI at a national level. The most common PSI was postoperative hemorrhage/hematoma (27.6%) and the highest cost by case was ...