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. Author manuscript; available in PMC: 2010 Sep 22.
Published in final edited form as: Addiction. 2003 Mar;98(3):269–279. doi: 10.1046/j.1360-0443.2003.00310.x

Figure 1.

Figure 1

Mean (SEM) percentages of urine specimens negative for the targeted drug (illicit opiates or cocaine) during the Baseline (B), Intervention (I), and maintenance (M) phase of each study. Vouchers were available during the Intervention phase only. Data are shown only for participants whose voucher earnings were contingent on abstinence, not for control participants who received vouchers noncontingently. For the Intervention and Maintenance phases, repeated-measures ANCOVAs controlling for Baseline use of the targeted drug showed no main effect of cannabis-use category and no interaction of cannabis-use category with time.