Relationship between follow-up rates and treatment outcomes in substance abuse research: more is better but when is "enough" enough?
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.
Hansten
M L
ML
Alcohol and Drug Abuse Institute, University of Washington, Seattle 98105, USA.
Downey
L
L
Rosengren
D B
DB
Donovan
D M
DM
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