0 - National Criminal Justice Reference Service

the equation. It clearly makes a large difference, therefore, whether an inmate successfuzzy
completes his treatment program or not.
We also examined whether the effects of TC varied by institution, since some differences
in TC implementation were observed at the five institutions. We entered a categorical variable that
reflected the effect of the institutional setting of each TC program (see Model 2 in Tables 17 and
18). None of these institutional effects were statistically significant, suggesting that the impact of
TC on reincarceration was invariant across the five institutions. Finally, we estimated
reincarceration rates using predicted probabilities fiom logistic regression equations (see Figure
2).,, TC resulted in a significantly reduced probability of reincarceration (19% v. 26%), even
when results were adjusted for the effects of control variables (see Table 18, Model 2).
Life tables for survival and risk (hazard) of reincarceration are shown in Table 19. For the
a
comparison group, there was a sizeable drop in cumulative survival fiom 92% to 76% between six
to 9 months following release fiom prison. Cumulative survival dropped gradually until the 15-
month interval, where it declined precipitously fiom 62% to 25%. This appears to be a
particularly high-risk interval, although there are currently too few cases in the longer time
intervals to make definitive conclusions about survival at this time. The hazard hction shown in
Figure 3 reveals the survival advantage enjoyed by TC inmates after 9 months.
0
34 Probabilities of reincarceration for the Comparison and TC groups were estimated using logistic
regression equations with all predictor and control variables entered: Prowevent) = (1 /( 1 + e-'),
where Z = C BkXik (Hanushek and Jackson, 1977; Lichter, 1989, Norusk, 1990). Estimated
probabilities show the likelihood of the event (e.g., reincarceration), holding all variables except
TC treatment at their means. These probabilities can be interpreted as the average effect of TC v.
Comparison group membership on the event if all other variables were the same. The same
procedures were used to estimate probabilities of rearrest and drug relapse for the TC and
Comparison groups.
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This document is a research report submitted to the U.S. Department of Justice. This report has not
been published by the Department. Opinions or points of view expressed are those of the author(s)
and do not necessarily reflect the official position or policies of the U.S. Department of Justice.