Lost to follow-up in the Norwegian mother, father and child cohort study.

Background The aim of pregnancy cohorts was to understand causes and development of health and disease throughout the life course. A major challenge in cohort studies is to avoid selection bias from loss to follow-up. Objective The aim of this study was to describe what characterises drop out from the Norwegian Mother, Father and Child Cohort Study (MoBa), and provide a resource to inform the interpretation of results from analysis of cohort data. Methods We estimated loss to follow-up in subsets of participants that responded to questionnaire waves in MoBa through an eight-year period and described characteristics of participants who responded to follow-ups. Within each wave of questionnai…