1988-09 -- 1989-02
For selected variables, statistical imputation was performed following logical imputation to replace missing responses. Unique code values (7, 8, or 9) were assigned to the recency-of-use variable when such logical imputation occurred. These code values are readily identifiable by the phrase "... LOGICALLY IMPUTED" in the code value descriptions. For those recency-of-use variables with missing data for which no indication of use of the drug could be found by examination of all relevant variables in the record, a code value of 91 ("Never Used") was assigned if there were one or more indications of such nonuse in the set of relevant variables.
To protect the anonymity of respondents, all variables that could be used to identify individuals have been deleted from the public use file.
Data were weighted based on the three stages of sampling that were used. The person-level sampling weight is the product of the three-stage sampling weights, each of which is equal to the inverse of the selection probability for that stage. Adjustments were made to compensate for nonresponse and sampling error. Adjustments also included trimming sample weights to reduce excessive weight variation and a post-stratification to Census population estimates.
For some drugs that have multiple names, questions regarding the use of that drug may be asked for each distinct name. For example, even though methamphetamine, methedrine and desoxyn are the same drug, their use was measured in three separate variables.
Data were collected by Research Triangle Institute, Research Triangle Park, NC, and prepared for release by National Opinion Research Center, Chicago, IL.