Follow-up
RECRUITMENT
Follow-up data were collected 6, 12, 18 and 24 months after recruitment using primarily computer-assisted telephone interviews (88%) and face-to-face interviews. Incentives consisting of vouchers for purchases of daily needs were sent out to participants before the follow-up at month 12 (5€) and after follow-up participation at months 6 (10€), 18 (15€), and 24 (20€). Overall, follow-up participation per time-point was 77–83%. The interviewers were not informed about group allocation. Of all computer-assisted telephone interviews, 64% were conducted by student interviewers (97/47/49/60% at months 6/12/18/24) and 36% by research assistants who were involved in recruitment 1–2 years earlier.