PUB 540 Describe the common characteristics and design of a case-control study

PUB 540 Describe the common characteristics and design of a case-control study

PUB 540 Describe the common characteristics and design of a case-control study

Case-control studies allow the investigator to measure exposure and outcome to study the outcome variables for both case and control.  Then the association between the control group and case groups are compared for similarities.  There are key selection criteria features when using this type of design. These are the key features as discussed by Setia (2016): 1) Case must be clearly well described to include all aspects of the selection criterion; 2) they need to come from the same group and the evaluation methods must be the same for both case and control group; 3) Matching can be used to ensure the case group and control group would be the same, for example with smokers, selection of the same age group and gender helps. One freedom is that where cases are collected is not a constraint.  Cases and control groups can come from clinics, hospitals, or medical registrars according to Kumar (n.d.).  All these factors mentioned are crucial as not create selection bias as also discussed by Setia (2016).

Case control studies are usually retrospective according to Kumar (n.d.), so selection bias can occur easily.  When selection bias occurs, it opens the door to groups that should be compared because the similarities may not be there.  And, if hospital cases are chosen, patients with higher exposure could produce skewed results.



Kumar (n.d.) Introduction to Study Designs – Case-Control Studies.  Health Knowledge Website.

Setia M. S. (2016). Methodology Series Module 2: Case-control Studies. Indian journal of dermatology61(2), 146–151.

Friis, R. H., & Sellers, T. (2020). Epidemiology for public health practice (6th ed.). Jones & Bartlett Learning.

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Case-control studies can be classified as analytical and observational studies. The common characteristic of a case control-study is an observational study that compares the infected individuals of a particular disease to those who are uninfected.  More scientifically the case represents those with the disease of interest, while the control represents those without the disease.  For the objective of the study to be effective and displayed one must utilize the three essential features for selecting cases and controls.  Control should be selected from the source population while cases are present or from the same study. Furthermore, matching techniques should be used to ensure cases and controls have the same features.  The third characteristic is the confounding elimination.

Case-control studies are notorious to bias due to the backward approach (Aigner et al., 2018). Therefore, researchers must define the case by providing an inclusion criterion. The limitation of questionnaire lacks the appeal to one ethos, not allowing for accurate responses, time consuming, and inaccurate recall. Other methods for collecting data are the following but no limited to records and interviews. These methods of data collection will allow for the researchers to develop more of a connection and understand the subjects.




Aigner, A., Grittner, U., & Becher, H. (2018). Bias due to differential participation in case-control studies and review of available approaches for Adjustment. PLOS ONE13(1). 


Kopec, J. A., & Esdaile, J. M. (1990). Bias in case-control studies. A review. Journal of epidemiology and community health44(3), 179–186.

A case-control study that compares patients who have a disease with patients who do not have the disease and looks back retrospectively (back in time to find the relative risk factors) 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, (Tenny et al., 2022).

The three essential features related to selecting cases and controls entail, identifying and or selecting individuals in

PUB 540 Describe the common characteristics and design of a case-control study
PUB 540 Describe the common characteristics and design of a case-control study

whom the distribution of exposure status would be the same as that of the cases in the absence of an exposure disease association, participants are based on their outcome status. The cases and controls should have the same distribution of exposure. It is essential that the case definition is clearly defined at the outset of the investigation to ensure that all cases included in the study are based on the same diagnostic criteria. The source of controls is dependent on the source of cases.  Situations where cases and controls can be violated through selection bias. According to Tenny et al., (2022) “The researcher must recognize the potential for failing to identify confounding variables or exposures, introducing the possibility of confounding bias, which occurs when a variable that is not being accounted for that has a relationship with both the exposure and outcome. This can cause a researcher to accidentally be studying something that is not accounted for but that may be systematically different between the groups, (Hennekens & Buring, 1987).


The limitations of using questionnaires in determining exposure status are that data collected might be time-consuming, and longer for participants complete questionnaires. Untruthful answers when filling out the questions and not fully understanding what is asked. Strategies for collecting information are to make sure questions are short, clear, and to the point. Make sure all questions are asked to address the aims of the research, (Mcleod, 2018).



Hennekens CH, Buring JE. Epidemiology in Medicine, Lippincott Williams & Wilkins, 1987. Introduction to study designs, case-control studies. Retrieved From:


Mcleod, S., (2018). Questionnaire: definition, examples, design, and types. Simply Psychology


Tenny, S., Kerndt, C. C., & Hoffman, M. R. (2022). Case-Control Studies. In StatPearls. StatPearls Publishing.

“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.” (GWU, 2019). However, “case-control studies, like cohort studies, can be either retrospective or prospective. In a prospective case-control study, the investigator still enrolls based on outcome status, but the investigator must wait to the cases to occur.” (BU, n.d.)

The three important features of a case-control study are: survivor sampling, case-based sampling and risk set sampling.

Survivor sampling is “Survivorship bias means that the researcher subjects variables to some sort of screening contest, and chooses the ones who sail through the process successfully. This pre-selection process pushes out unsuccessful variables due to their lack of visibility. When survivorship bias happens, the entire spotlight beams on the most successful variables, even if these participants do not have relevant information for the study. Expectedly, this can affect the validity of your research results. Survivorship bias also tends to create conclusions that are overly optimistic, and that may not be representative of real-life environments.” (Formplus, 2022).

Case-based sampling “This sampling involves using controls selected from the source population such that every person has the same chance of being included as a control. This type of sampling only works with a previously defined cohort. In these case-control studies, the odds ratio provides a valid estimate of the risk ratio without assuming that the disease is rare in the source population.” (Alexander, et al, 2013).

Risk-Set sampling “When cases are incident cases and when controls are selected from the at-risk source population at the same time as cases occur (controls must be eligible to become a case if the health outcome develops in the control at a later time during the period of observation) then we call this type of sampling incidence density sampling or risk set sampling. The control series provides an estimate of the proportion of the total person-time for exposed and unexposed cohorts in the source population. In these case-control studies, the odds ratio estimates the rate ratio of cohort studies, without assuming that the disease is rare in the source population.” (Alexander, et al, 2013).

In my opinion I can clearly see errors and bias occurring with risk-set sampling. Selecting subjects from the same group of the “at risk” group, during the same time frame. i believe this can tilt the odds ratio in the positive favor of the hypothesis answer the researcher is seeking.

Limitations of using questionnaires for exposure status would be the following: “can not be considered for illiterate persons, Validity and reliability is low, Poor and late responses, Not helpful in finding information of the complex emotional person and It allows respondents to change their previous answer if it contradicts the after answers. (Prasanna, 2022).

A better alternative would be interviews. Interviews face to face, over the phone or online (zoom). This type of data collection for case control studies would yield honest and informative answers for the study. It allows the researcher to better understand the subject answers by observing their behaviors and allow them to express their opinions of the study. (VT, 2018).


Alexander, L., Lopes, B., Riccetti-Masterson, K., Yeatts, K. (2013). Case-control studies

Boston University School of Public Health. (n.d.). A nested case-control study.

Formplus Blog. (2022). Selection bias in research: types, examples and impact.

George Washington University. (2019). Case control – study design 101

Prasanna. (2022). Advantages and disadvantages of questionnaire: top 6 questionnaire advantages and

disadvantages: pros and cons.

Virginia Tech University, (2018). Research methods guide: interview research.