PURPOSE

There is a trend of decreasing response rates in population surveys, and selective nonresponse represents a major source of potential bias in population-based survey estimates of drug use behaviors, especially estimates based on longitudinal designs.

METHODS

This study compared baseline substance use behaviors among initial respondents who did respond (n = 34,653) and did not respond (n = 8440) to a 3-year follow-up interview in a prospective study of the general U.S. adult population. Differences in nonresponse rates were assessed as a function of past-year drug use behaviors both before and after adjustment for socio-demographic differences potentially associated with these behaviors, and the effects of interactions of the socio-demographic characteristics with the drug use behaviors were assessed in multivariate logistic regression models for response at the 3-year follow-up.

RESULTS

Weighted and unweighted nonresponse rates varied between alcohol users and users of other drugs such as cocaine and marijuana, with rates of nonresponse being higher in the latter drug categories. There were also significant differences in nonresponse rates as a function of frequency of use and demographics. More specifically, being married tends to reduce the probability of non-response, while older age, being male, being Asian or Hispanic, and having lower education all substantially increase the probability of nonresponse at Wave 2, even after controlling for relevant covariates.

CONCLUSIONS

This study provides the substance abuse field with a methodology that users of longitudinal data can apply to test the sensitivity of their inferences to assumptions about attrition patterns.