Table 3.

Factors to Consider in the Design and Analysis of Case-Crossover Studies

Factor	Yes	No	Uncertain
Did the exposure or hazards periods of risk make reasonable biologic and/or clinical sense?	□	□	□
Have the investigators made attempts to independently validate the exposure factor(s) of interest?	□	□	□
Have an adequate number of incident cases been selected and are only persons with an initial disease event being studied?	□	□	□
Was effect modification potentially taking place in various pre-defined subgroups?	□	□	□
Was there potential for recall bias of the key exposure factor of interest?	□	□	□
Were patients interviewed at an appropriate time in their course of disease and setting to give as accurate a set of responses as possible?	□	□	□
Have differences in absolute from relative risk been clearly distinguished?	□	□	□
Were the study findings clearly presented and adequately interpreted?	□	□	□
Were the study strengths and limitations clearly acknowledged?	□	□	□