At study completion we had sent invitation letters followed by phone call to 3314 potential controls. Traced eligible subjects were 2774, of whom 2012 accepted to participate. Completion rate was 60.7% (subjects who accepted to participate/contacted subjects) and participation rate was 72.5% (subjects who accepted to participate/eligible subjects). Moreover, we sent pre-stamped return-cards to 393 subjects whom we were unable to trace through the phone. Of these, 155 were eligible, and 108 accepted to participate (completion rate = 27.5%, participation rate = 69.7%). Overall, we enrolled 2120 controls, with an overall participation rate of 72.4%. Epidemiological data and DNA samples were collected from 99.8% and 99.9% of controls, respectively (Table 1).
