Case-control Study

Case-control Study

Describe the common characteristics and design of a case-control study. Discuss the three
important features when it comes to selecting cases and controls, and identify a situation
when one of these might be violated. Discuss the limitations of using questionnaires for
determining exposure status and provide examples of alternative strategies for collecting
this information in a case-control study.

Case-control Study

According to Mahajan (2015), the collective characteristics and design of the case-control
study entail the enrolment of people who have a particular disease or outcome and sampling a
second control group of similar size from an identical population. The acquisition of the relevant
information occurs through comparing patients presenting with a particular illness or outcome of
interest (cases) with those who do not have signs and symptoms of the condition (controls). It
further involves tracing back retrospectively in time to compare the frequency of the exposure to
a risk factor in each group to determine its correlation with the disease (Mahajan, 2015).
Moreover, it focuses on the estimation of the odds of an individual developing an illness or
experiencing a specific event. Subsequently, the information regarding the participant’s exposure
to risk factors is calculated through the odds ratio.

The three essential features related to the selection of cases and controls entail the
identification and classification of cases from the source population in terms of whether they
belong to the exposed or unexposed cohort. Subsequently, the sampling of a second control
group is conducted in a similar size from a population identical in every aspect to that of the
cases (Mahajan, 2015). Nevertheless, since the control group is used in the estimation of the
distribution of exposure in the source population, selection and sampling of the control group
with the inclusion of the exposure status would lead to violation of the cardinal requirement.
Most fundamentally, in a case-control study, the limitation of using a questionnaire in the
determination of the exposure status include difficulty in finding a suitable control group as some
respondents tend to provide misleading or inconclusive information on whether they have a
disease or not. Additionally, using questionnaires in determining the exposure status is associated
with a differential recall bias in the quality of data obtained that adversely impacts the study by
suggesting an artificial relation. However, to avoid such challenges, for instance, an alternative
strategy for determining the exposure status entails the random selection of a sample and asking
them to participate through a phone survey (Mahajan, 2015). This way, the differential recall
bias would be eliminated through the verification of the relevant information.



Mahajan, A. (2015). Selection bias: Selection of controls as a critical issue in the interpretation
of results in a case control study. Indian Journal of Medical Research, 142(6), 768.

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