The majority (53) of the 68 key variables were categorical, with four possible response categories: “yes,” “no,” “obligate no,” and “missing.” The SSADDA skipped out of the cocaine section when the respondent reported never having used cocaine more than 10 times (lifetime), and subsequent categorical items in the cocaine section were scored as “obligate no” and subsequent continuous items as “obligate missing;” these form their own categories in our analysis. About 1.1% of the data on the 68 key variables were missing for the 9,965 subjects. Thus, there were 312 possible categories for the 68 key variables.
