Percentage of participants who were cocaine abstinent at three follow-up visits occurring 3, 6, and 12 months after the final maintenance dose of methadone. Statistical results are from a generalized linear mixed model (SAS GLIMMIX macro) that does not require imputation of missing data. However, the data shown are actual percentages, with missing specimens ignored; in other words, the denominator at each time point is the number of specimens actually collected (see legend for ns). CM = contingency management; CBT = cognitive–behavioral therapy; DSM–III–R = Diagnostic and Statistical Manual of Mental Disorders (3rd ed., rev.; American Psychiatric Association, 1987); Dep = dependence.