Reliability and validity of 6-month timeline reports of cocaine and heroin use in a methadone population.

Fifty-nine persons addicted to heroin and maintained by methadone reported on daily heroin and cocaine use during 2 timeline calendar interviews administered 6 weeks apart. Retrospective reports covering 6 months were compared with urine samples taken weekly during the interval. Test-retest correlations were high and timeline estimates of drug use frequency were significantly correlated with the frequency of drug-positive urine results. Thus, timeline reports of drug-use frequency appeared both reliable and valid. Individual participants either over- or under-reported by an average of about 15%, and they did not identify instances of drug use with greater than chance accuracy when particular episodes of drug use occurred. These results support the use of timeline reports to make group comparisons of long-term drug use, but suggest that timeline data should not be used to identify specific drug-use episodes. Work with other drug-use population is necessary to extend these conclusions.