As with any other type of study, the specific hypothesis under
investigation must be clearly stated before a case–control study is designed
in detail. Failure to do this can lead to poor design and problems in interpretation
of results. Case–control studies allow the evaluation of a wide
range of exposures that might relate to a specific disease (as well as
possible interactions between them). clearly illustrates this
feature.
Case–control studies often constitute one of the first approaches to
study the etiology of a disease or condition, as in . This is
partly because of their ability to look at a wide range of exposures and
partly because they can be conducted relatively cheaply and quickly.
The results from these exploratory case–control studies may suggest specific
hypotheses which can then be tested in specifically designed studies.
Precise criteria for the definition of a case are essential. It is usually
advisable to require objective evidence that the cases really suffer from
Chapter 9
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Example 9.2 (Not Exposed) (Control อาจมีจำนวนเท่ากับ Case หรือมีจำนวนเพิ่มเป็น 2 เท่า)