title: Participants who left a multiple-wave cohort study had similar baseline characteristics to participants who returned.
abstract: OBJECTIVE
  Research on determinants of an individual's pattern of response, considered as a profile across time, for cohort studies with multiple waves is limited. In this prospective population-based pregnancy cohort, we investigated baseline characteristics of participants after partitioning them according to their history of response to different interview waves.
  
  
  METHODS
  Data are from the Mater-University of Queensland Study of Pregnancy 1981 to 1983 cohort, Brisbane, Australia. Complete baseline information was collected for 7223 of 7535 eligible individuals (95.9%). Follow-up occurred at 6 months, 5 years, and 14 years. Response rates were 93.0%, 72.5%, and 71.8%. Participants were allowed to leave and reenter the study. Participants were categorized as always, intermittent, or never responders. Intermittent responders were categorized further as leavers (responded at least once before leaving the study) or returners (left the study before reentering).
  
  
  RESULTS
  Participants who always responded were older, more educated, married, Caucasian, and nonsmokers and had higher incomes. Intermittent responders shared similar baseline characteristics. Relative risk for being an intermittent responder was located between risks for always or never responding.
  
  
  CONCLUSIONS
  Participants who left and reentered the study had baseline characteristics similar to participants who responded at least once and then left the study.
authors.affiliation: School of Population Health, The University of Queensland, Brisbane, Australia. r.ware@uq.edu.au
authors.forename: Robert S
authors.initials: RS
authors.lastname: Ware
authors.forename: Gail M
authors.initials: GM
authors.lastname: Williams
authors.forename: Rosemary L
authors.initials: RL
authors.lastname: Aird
mesh_terms: D000293:Adolescent; D000328:Adult; D015982:Bias; D015331:Cohort Studies; D005260:Female; D005500:Follow-Up Studies; D006306:Health Surveys; D006801:Humans; D008875:Middle Aged; D010352:Patient Dropouts / Q000706:statistics & numerical data*; D011247:Pregnancy; D012106:Research