Dwelling unit listings were selected using systematic sampling. The sampled listings were then sent to the field for screening. This roster formed the basis for the within-dwelling sampling of individuals. Introductory letters are sent to sampled addresses, followed by an interviewer visit. This selection process is designed to provide the necessary sample sizes for specified population groups by selecting up to two persons per household, depending on the composition of the household.
Interviewers attempt to conduct the survey in a private place, away from other household members.
In the latter, the answers to sensitive questions, such as those dealing with illicit drug use, are recorded by the respondent and not seen or reviewed by the interviewer. After the self-administered answer sheets are completed, they are placed by the respondent in an envelope, which is sealed and mailed to the contractor with no personal identifying information attached. Upon receipt, questionnaires are checked for critical identification and demographic data, then keyed to disk. This creates a file consisting of one record for each completed interview. Extensive within-record consistency checks and resolution of most inconsistencies and missing data are done using machine editing routines, called logical imputation.