Abstract

The participation rates in epidemiologic cohort studies have declined in recent decades. We aimed to evaluate the effect of home recruitment on participation rate and non-response bias within the individuals with psychosis in a follow-up study. The baseline (1999–2001) and follow-up (2008–2010) studies in the Northern Finland Birth Cohort 1966 consisted of magnetic resonance imaging of the brain, cognitive testing and psychiatric assessment. The participation rates were 67% (54/81) for baseline participants, 10% (5/49) for baseline non-participants and 35% (48/136) for those who were diagnosed with a psychosis after the baseline study. In order to increase participation of the individuals who had participated at the baseline (n=81), those who would not have participated otherwise were offered to be interviewed at home. Altogether 18 follow-up participants were home-recruited. Several illness-related variables were compared between the home-recruited participants, standard protocol participants and non-participants. The home-recruited participants had more symptoms, lower functioning, cognition and total grey matter volume, and higher use of antipsychotics measured at baseline (absolute values of effect sizes 0.60–1.05), compared to standard protocol participants and non-participants. The same differences occurred between the home-recruited and standard protocol participants in the follow-up. By using home recruitment we were able to increase the participation rate and to avoid problems of non-response bias. Effective recruitment may need special efforts in population-based studies for individuals with psychosis.