important assumptions in a case crossover design include that the exposure
should be brief, the time between exposure and event onset should be short
and there is little carryover effect on the exposure. Therefore, this study
design canít be used, for example, to evaluate an intervention which is
anticipated to cause cumulative changes in the participants, or to study on
the progression of a chronic disease.
- Because of the above conditions, the results from a case crossover
analysis only represent short-term risk but not cumulative risk, and
relative risk but not absolute risk.