For example, children awaiting adoption may be interviewed while on the waiting list, then again after a match has been made, and then again when they have been placed with a family. Panel designs contrast with cohort studies, in which a group is studied over time but different members may be the individual study participants each time. For example, former users of substance abuse treatment programs may be surveyed at 3 months, 6 months, and 12 months after discharge, but the surveys may go to different members of each cohort for each time period.