title: Relationship between follow-up rates and treatment outcomes in substance abuse research: more is better but when is "enough" enough?
abstract: OBJECTIVE
  To examine the effects of different follow-up rates on estimates of treatment outcome and predictive models thereof, and to specify participant characteristics associated with tracking difficulty.
  
  
  METHODS
  An observational study using data collected for a randomized, experimental design.
  
  
  METHODS
  The King County Assessment Center in Seattle, Washington, an organization responsible for referral to publicly funded substance abuse treatment.
  
  
  METHODS
  Substance-addicted individuals referred to publicly funded inpatient or outpatient treatment.
  
  
  METHODS
  Standardized self-report instruments measuring substance use, substance use consequences and general functioning. Chart review was used to measure treatment entry and completion.
  
  
  RESULTS
  There was a significant association between follow-up difficulty and outcomes related to addiction treatment and later substance use. However, outcome estimates based on 60% of the sample who were easiest to locate were only minimally different from those based on the 90-100% ultimately captured, and predictive models of outcome based on the 60% group were reasonably similar to those based on the final sample. Of baseline characteristics examined, only age was associated with later tracking difficulty.
  
  
  CONCLUSIONS
  Studies reporting follow-up rates below 70% may produce valid findings and study attrition may be largely unpredictable from participant characteristics at baseline. However, a number of factors such as type of population studied, geographical location of the sample, reasons for loss to follow-up and sample size must be considered when attempting to generalize the findings of this study.
authors.affiliation: Alcohol and Drug Abuse Institute, University of Washington, Seattle 98105, USA.
authors.forename: M L
authors.initials: ML
authors.lastname: Hansten
authors.forename: L
authors.initials: L
authors.lastname: Downey
authors.forename: D B
authors.initials: DB
authors.lastname: Rosengren
authors.forename: D M
authors.initials: DM
authors.lastname: Donovan
mesh_terms: D000328:Adult; D000367:Age Factors; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D008297:Male; D010352:Patient Dropouts; D012107:Research Design; D012307:Risk Factors; D018401:Sample Size; D019966:Substance-Related Disorders / Q000628:therapy*; D016896:Treatment Outcome