The quantity-frequency index was based on the number of days a particular drug was used, summed across 12 drugs: alcohol, marijuana, hallucinogens, crack, cocaine, heroin, inhalants, quaaludes, barbiturates, tranquilizers, amphetamines, and other opiates.
On the quantity-frequency index, the distribution curve for those reporting AOD use at pretest had a natural break that separated the experimental users (33%) from the users/abusers (28%).
The 132 new intervention youth showed larger decreases in AOD use on the quantity-frequency index (ES = .44) and on the number-of-drugs index (ES = .51) than did the 47 adolescents who reentered the program (quantity-frequency index, ES = .14; number-of-drugs index, ES = .25).
The change score on the two AOD indexes was the dependent variable for two separate sets of multiple regression analyses, one based on the quantity-frequency index and the other on the number-of-drugs index, both continuous variables.
The dependent variables, or outcome measures, were the categorical success measures: success1, based on change in score on the quantity-frequency index, and success2, based on change in score on the number-of-drugs index.
Although males reported higher overall AOD use, it was not significant for either the quantity-frequency index ([t.sub.311] = 1.69, p = .92) or the number-of-drugs index ([t.sub.412] = 1.37, p = .172).
The 132 panel intervention youth showed a highly significant reduction in AOD use from pretest to posttest (correlated t test) as measured by the quantity-frequency index ([t.sub.262] = 4.25, p = .000) and the number-of-drugs index ([t.sub.262] = 4.99, p = .000).
The difference between groups in terms of reduction in AOD use was highly significant for the quantity-frequency index ([t.sub.130] = 3.32, p = .001), as well as significant for the number-of-drugs index ([t.sub.130] = 2.l4, p = .035).
Results for the quantity-frequency index (change score) were highly significant: dosage (p = .0001), level of use at pretest (p = .0000), and site (p = .0000).
Logistic regression analysis based on that sample showed the ACI to be a better predictor of a total score of self-reported alcohol related problems than the CAGE questionnaire, the quantity-frequency index, subjective problem self-ratings and other selected descriptive factors (O'Hare and Tran, 1997).
Chronbach alphas in both samples were comparable (socio-emotional .88, .89; community .79, .76), and the CAPS demonstrated good concurrent validity with the quantity-frequency index, a version of the MAST, and peak drinking index from the AUDIT (O'Hare, 1997; O'Hare, 1998).