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Appendix E Construction of Exposure , Outcome , and Risk Score Indices

The general exposure index, described in Section E.1.1, is based on questions that ask about exposure to anti-drug media messages through a variety of channels. The specific exposure index, described in Section E.1.2, is based on the specific National Youth Anti-Drug Media Campaign (Campaign) ads being broadcast during the 60 days prior to the respondent’s interview. Since each respondent was asked about recall of only a limited number of the ads, responses to the nonsampled ads were imputed for the construction of the specific exposure index if they were eligible for inclusion. Section E.1.3 presents evidence for the validity of the television ad recall measures for youth.