THE CONSISTENCY OF ESTIMATES OBTAINED THROUGH CENTRAL-LOCATION SAMPLING - ANALYSIS OF THE PARTNERSHIP FOR A DRUG-FREE AMERICA ATTITUDE TRACKING STUDY

To evaluate the reliability and validity of estimates of drug use obta ined through multiple-site central-location sampling, data from the Pa rtnership Attitude Tracking Study (PATS), collected annually beginning in 1987, are tracked longitudinally and Compared with data collected through traditional household interviews. Comparisons with demographic estimates from Current Population Surveys indicate that central-locat ion sampling can provide a broadly representative sample of the adult population. However, there is some coverage bias in central-location s ampling; most notably in the underrepresentation of adults who do not have high school diplomas. Sample estimates obtained from central-loca tion sampling are consistent over time. Basic demographic characterist ics of the samples-education, income, marital status, and area of resi dence-vary by less than 5% across the four waves of the tracking study . Prevalence estimates of self-reported drug use demonstrate an even h igher degree of consistency over time. Comparisons of PATS and Nationa l Household Survey of Drug Abuse data and the Monitoring the Future da ta indicate a higher level of drug use and a lower level of perceived risk of occasional use among PATS respondents. While the trends in use and perceived risk reported in all studies are similar, we suggest th at perceived threats to confidentiality and anonymity often result in significant underreporting of drug use, particularly in household surv eys. Sample estimate differences are attributed to sampling and measur ement error. Some discrepancy in prevalence estimates is associated wi th the fact that the PATS sample is not a true probability sample; as a result, the sampling error of the overall study cannot be estimated precisely. It is also likely that the difference in estimates between the studies is a product of the decreased measurement error of PATS me thodology. In central-location sampling, respondents are completely an onymous and may feel more comfortable in providing honest answers abou t illicit activities such as drug use. The potential applications of t his methodology are discussed.