Respondent interviews included a number of use-related questions, and the appearance-based and
demographic information. Further, in addition to their own personal information and telefunken code, each respondent was asked to select up to five methamphetamine-using contacts whose phone number they currently had in their mobile phone’s directory. This selection was carried out by choosing initial letters of last names from a randomized list of alphabet letters. The respondent was then questioned about the randomly selected contacts, in order to obtain data on the contacts’ personal characteristics (approximate height, approximate weight, hair color, eye color, gender, and race/ethnicity) and telefunken code.