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Drug testing data received for 947 parolees were the most thorough and complete (i.e.,
fewest missing cases). Relapse analyses examined 189 inmates in the Experimental (TC) group,
and 529 inmates in the Comparison Sample characteristics are presented in Table 26.
The TC and Comparison groups did not differ on amount of time at risk since their release
fi-om prison (Table 24). As expected, the TC group had a mean total treatment exposure nearly 15
times as great as the Comparison group. The two groups differed on a number of other selection
i
criteria, once again indicating the need to use either matching or statistical controls to control for
selection bias. Because only a portion of inmates in the sample (especially TC graduates) had been
released fi-om prison so far, we preferred the use of statistical controls to matching in order to
minimize the loss of cases.
a
Using logistic regression, we examined the impact of TC on drug relapse rates, controlling
for selection differences (Tables 25 and 26). Control variables included prior and current criminal
history, time remaining to minimum sentence at the time of program admission, age, standardized
drug score, and membership in either the TC or Comparison group. Inspections for
multicollinearity among the variables to be entered in the analyses revealed no daculties. No
correlation exceeded .40.
The first table (Table 25) once again shows results for all released offenders; the second
table (Table 26) restricted the analyses only to inmates who successfully completed their
treatment program. In the fmt model examined in both tables (i.e., without the effects of
institutional setting or employment entered), nothing except the amount of time at risk since
release fiom prison significantly predicted drug relapse. In both analyses (all discharges v.
38 As with other outcome analyses, a time at risk of six months or greater since release
fi-om prison was used to select cases, and we excluded inmates whose "release" was artificial (i.e.,
114
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been published by the Department. Opinions or points of view expressed are those of the author(s)
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