Outcome time frames for this report varied from 4 weeks to 53 weeks depending on the date of participant recruitment. On average, the outcome period was 21 weeks. t-tests and chi-square analyses were used to test for differences between intervention conditions. ICM was significantly more effective than CC in facilitating treatment entry: 88% of clients in ICM entered substance abuse treatment versus 65% in CC (p < .001). Overall, 46% of the sample was assigned to receive inpatient treatment: either detoxification or brief residential treatment. ICM and CC did not significantly differ in rates of entry to inpatient treatment (78% versus 69%). All participants were assigned to outpatient treatment either directly or following inpatient care. Differences were significant for outpatient treatment: 86% of clients in ICM entered outpatient treatment versus only 53% in CC (p < .001).
In addition, ICM was significantly more effective in retaining participants in treatment. Clients in ICM attended 42% of the days they were assigned to treatment versus 22% of days for clients in CC (p < .0001). Differences were especially marked for outpatient treatment. On average, ICM clients attended about five times more outpatient sessions (M=29.7, SD=30) than clients in CC (M=6.6, SD=13). Differences were significant even when comparing only clients who entered outpatient treatment: ICM clients attended M=34.5 (SD=29) sessions, versus M=12.3 (SD=15.7) for CC clients (p < .0001).