On Correcting Biases in Self-Reports of Age at First Substance Use with Repeated Cross-Section Analysis.

Household survey data on age at first use of alcohol, tobacco, marijuana, and hard drugs can be biased due to sample selection and inaccurate recall. One potential concern is attrition, whereby individuals who get involved with substance use at an early age become increasingly less likely to be surveyed in successive years. A comparison of data from the National Household Survey on Drug Abuse (NHSDA) with data from a longitudinal study suggested that attrition might have caused substantially less bias than did "forward telescoping," the inflating of age at first use over time. The evidence of forward telescoping was particularly pronounced with respect to age at first use of alcohol. This paper presents a procedure for correcting the distribution of age at first use for forward telescoping (but not attrition) by viewing a portion of the NHSDA data collected in successive years as constituting a cohort study. Results are presented from applying this procedure with NHSDA data collected from 1982 to 1995 for respondents born 1968-1973. The findings suggest that prevention programs need to be introduced at an earlier age than would be indicated by "uncorrected" retrospective data. Other implications are also highlighted.