Question

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.

Answer 1

3 Features:

• Deconfounding and efficiency are the main concerns in considering some special sample techniques including matching or cluster sampling.
• The controls should be representative of the source population.
• The 'controls' must be sampled in a way thatthi should not be more or less likely if they have exposure to interest.

In situation when one of these is violated we need to check the behaviour of estimate under these conditions.

Limitations of using questionnaires for determining exposure status.-

• Respondents not being truthful affecting efficiency whether yes or no. misunderstanding question.
• Recall bias due to it relying on the subjects ability to recall past exposures.
• Differential recalls between the cases and control can introduce bias and effect studies by suggesting an artificial relation.

Examples of alternative strategies:

A retrospective study. Eg A control group of people who do not have the bone fracture or the one whi has not experienced it is used for comparison.