Survey estimates of drug-use trends in urban communities: general principles and cautionary examples

Surveys to depict substance abuse rates and monitor trends in specific areas have become increasingly important policy tools. Yet, as illustrated by two national multiwave surveys, using small sample survey data and making longitudinal comparisons is fraught with interpretative problems. In the case of the metropolitan area "oversample" of the National Household Survey on Drug Abuse, for example, interpreting apparent declines in drug use has to take account of the devastating effects of Hurricane Andrew in the Miami Metropolitan area. In the case of a 41-community survey sponsored by the Robert Wood Johnson Foundation to evaluate substance abuse prevention, the difficulty is how to interpret small differences in drug use, which seem to follow no reasonable pattern with respect to treatment or comparison sites. Inferences from such surveys are confounded with statistical anomalies and unforeseen events. They are limited by the sample size. In part, the solution to these problems is to use other survey and nonsurvey data to validate their conclusions and to note their limitations.