title: Assessing bias in a prospective study of diabetes that implemented substitution sampling as a recruitment strategy.
abstract: OBJECTIVE
  Strategies such as reminders are frequently used to maximize baseline recruitment and for this reason are collectively termed "usual practice." The objective of this study was to investigate substitution sampling as an alternative recruitment strategy.
  
  
  METHODS
  Data are from the Living with Diabetes Study, which is a prospective cohort study providing a comprehensive examination of health care utilization. Baseline information was collected for 3,197 of 11,470 eligible individuals between November 2008 and October 2009. Follow-up occurred 12 months after recruitment, with outcome of interest being emergency department attendance. Biases resulting from the two recruitment programs were investigated through the comparison of adjusted logistic regression coefficients and absolute relative biases (ARBs).
  
  
  RESULTS
  Corresponding estimates resulting from both programs were similar except for age (75+ years). This effect was significant (β: -0.59; 95% confidence interval [CI]: -1.04, -0.13) under substitution sampling, but not under "usual practice" (β: -0.36; 95% CI: -0.78, 0.07). Analysis using the ARB metric reinforced similarity, with the Wilcoxon signed-rank test failing to detect significant difference between programs (median difference: -1.01; 95% CI: -5.88, 2.02).
  
  
  CONCLUSIONS
  Substitution sampling deserves consideration as a recruitment option alongside "usual practice," as concerns about additional bias may be unwarranted.
authors.affiliation: School of Population Health, The University of Queensland, Herston Road, Herston 4006, Queensland, Australia. Electronic address: michael.david@uqconnect.edu.au.
authors.forename: Michael C
authors.initials: MC
authors.lastname: David
authors.affiliation: School of Population Health, The University of Queensland, Herston Road, Herston 4006, Queensland, Australia.
authors.forename: Robert S
authors.initials: RS
authors.lastname: Ware
authors.affiliation: School of Population Health, The University of Queensland, Herston Road, Herston 4006, Queensland, Australia.
authors.forename: Rosa
authors.initials: R
authors.lastname: Alati
authors.affiliation: Health Quality and Complaints Commission, Level 17, 53 Albert Street, Brisbane 4000, Queensland, Australia.
authors.forename: Jo
authors.initials: J
authors.lastname: Dower
authors.affiliation: Cancer and Population Studies Unit, The Queensland Institute of Medical Research, Herston, Road, Herston 4006, Queensland, Australia.
authors.forename: Maria
authors.initials: M
authors.lastname: Donald
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D015982:Bias; D016001:Confidence Intervals; D003920:Diabetes Mellitus / Q000628:therapy*; D005260:Female; D006801:Humans; D016015:Logistic Models; D008297:Male; D008875:Middle Aged; D018579:Patient Selection; D011446:Prospective Studies; D055815:Young Adult
keywords: Bias; Prospective cohort study; Recruitment; Reminders; Responders; Substitution sampling