title: Attrition in a longitudinal study with hard-to-reach participants was reduced by ongoing contact.
abstract: OBJECTIVE
  Minimizing attrition is a key objective in longitudinal research, with possible consequences being additional bias and reduced generalizability. Identifying determinants of attrition is essential in determining attrition prevention strategies. The objective of this study was to investigate a number of these determinants, with an emphasis on contactability.
  
  
  METHODS
  Data were taken from the Passports project, a randomized controlled trial of an intervention to provide postrelease support to ex-prisoners in Queensland, Australia. Measures of contactability included intervention intensity, baseline collaterals, and follow-up telephone calls, with attrition at follow-up being the outcome event. Multivariable modeling was used to assess the independent effects of these measures on attrition.
  
  
  RESULTS
  Attrition was found to be more likely among those who were not contacted between the release and follow-up (adjusted odds ratio [AOR]: 2.93; 95% confidence interval [CI]: 1.87, 4.60), did not provide collaterals (AOR: 2.58; 95% CI: 1.68, 3.97), and received more than four telephone calls (AOR: 2.42; 95% CI: 1.61, 3.63). Evidence of dose-response relationships between attrition and the measures of collaterals and telephone calls was also seen to exist.
  
  
  CONCLUSIONS
  These findings have implications for sample size maintenance, especially those involving hard-to-reach populations. Subject to cost constraints and possible diminishing returns, researchers should endeavor to implement a study protocol that facilitates continued contact during follow-up.
authors: School of Population Health, The University of Queensland, Herston Road, Herston, Queensland 4006, Australia. michael.david@uqconnect.edu.au
authors: Michael C
authors: MC
authors: David
authors: Rosa
authors: R
authors: Alati
authors: Robert S
authors: RS
authors: Ware
authors: Stuart A
authors: SA
authors: Kinner
mesh_terms: D000223:Adaptation, Psychological; D000293:Adolescent; D000328:Adult; D000367:Age Factors; D000704:Analysis of Variance; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D007398:Interpersonal Relations; D016015:Logistic Models; D008137:Longitudinal Studies / Q000379:methods*; D008297:Male; D008875:Middle Aged; D015999:Multivariate Analysis; D010358:Patient Participation / Q000379:methods*; D018579:Patient Selection; D011329:Prisoners; D011793:Queensland; D012107:Research Design; D018570:Risk Assessment; D018401:Sample Size; D012657:Self-Help Groups; D012737:Sex Factors; D013997:Time Factors; D055815:Young Adult