title: Diverse recruitment strategies result in different participation percentages in a web-based study, but in similar compliance.
abstract: OBJECTIVE
  We compared participation and compliance with a web-based data collection on infections among population-based samples recruited in different ways.
  
  
  METHODS
  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).
  
  
  RESULTS
  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 %).
  
  
  CONCLUSIONS
  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.
authors.affiliation: Department of Epidemiology, Helmholtz Centre for Infection Research, Brunswick, Germany. manas.akmatov@twincore.de.|TWINCORE Centre for Experimental and Clinical Infection Research, Hannover, Germany. manas.akmatov@twincore.de.
authors.forename: Manas K
authors.initials: MK
authors.lastname: Akmatov
authors.affiliation: Department of Epidemiology, Helmholtz Centre for Infection Research, Brunswick, Germany.
authors.forename: Nicole
authors.initials: N
authors.lastname: Rübsamen
authors.affiliation: Department of Epidemiology, Helmholtz Centre for Infection Research, Brunswick, Germany.
authors.forename: Anja
authors.initials: A
authors.lastname: Schultze
authors.affiliation: Department of Epidemiology, Helmholtz Centre for Infection Research, Brunswick, Germany.
authors.forename: Yvonne
authors.initials: Y
authors.lastname: Kemmling
authors.affiliation: University Cancer Center Hamburg, University Medical Center Hamburg-Eppendorf, Hamburg, Germany.
authors.forename: Nadia
authors.initials: N
authors.lastname: Obi
authors.affiliation: Department of Epidemiological Methods and Etiologic Research, Leibniz Institute for Prevention Research and Epidemiology-BIPS, Bremen, Germany.
authors.forename: Kathrin
authors.initials: K
authors.lastname: Günther
authors.affiliation: Department of Epidemiological Methods and Etiologic Research, Leibniz Institute for Prevention Research and Epidemiology-BIPS, Bremen, Germany.
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Ahrens
authors.affiliation: TWINCORE Centre for Experimental and Clinical Infection Research, Hannover, Germany.
authors.forename: Frank
authors.initials: F
authors.lastname: Pessler
authors.affiliation: Department of Epidemiology, Helmholtz Centre for Infection Research, Brunswick, Germany.
authors.forename: Gérard
authors.initials: G
authors.lastname: Krause
authors.affiliation: Department of Epidemiology, Helmholtz Centre for Infection Research, Brunswick, Germany.
authors.forename: Rafael T
authors.initials: RT
authors.lastname: Mikolajczyk
mesh_terms: D000328:Adult; D000368:Aged; D035843:Biomedical Research / Q000379:methods*; D003141:Communicable Diseases; D005260:Female; D005858:Germany; D006801:Humans; D020407:Internet; D008297:Male; D008875:Middle Aged; D010349:Patient Compliance; D018579:Patient Selection; D011446:Prospective Studies; D011634:Public Health; D011795:Surveys and Questionnaires
keywords: Compliance; German National Cohort; Longitudinal study; Non-responders; Population-based study; Recruitment strategies; Response; Second-stage non-response; Web-based study