Diverse recruitment strategies result in different participation percentages in a web-based study, but in similar compliance.

Abstract

We compared participation and compliance with a web-based data collection on infections among population-based samples recruited in different ways. Individuals were recruited from participants in the German National Cohort study (Group A, n=279) or persons who were invited to this study but did not participate (Group B, n=53). A third group was invited to the web-based study only (Group C, n=145). Response varied among groups between 3% (B), 11% (C) and 61% (A), but compliance was similar (81-85%). Response did not differ by age and sex. Compliance was lower among the youngest and oldest participants. In addition, participants currently not employed were more likely to have better compliance. Semi-parametric group-based modelling identified three distinct compliance trajectories; "poor compliance" (8%), "improving compliance" (14%) and "very good compliance" (78%). Participation differed among modes of recruitment, but compliance was similar among groups and notably high. Different recruitment approaches can be used and collected data can be combined to achieve greater sample sizes for longitudinal web-based studies.