other type of control data they used is the patientís usual frequency of
physical exertion over the past year. The idea is to compare the amount of
time exposed to exertion and the amount of time not exposed to exertion over
the past with the information of whether there was exertion during the
hazard period. Since here "person-time" exposed to exertion is used, the
design is rather like a "cohort" study than a traditional case-control
study, and the analysis for this type of control data will also be more like
a cohort study analysis.