"Regarding criminal acts that were officially detected, 52 percent of drug court offenders compared with 62 percent of comparison offenders were re-arrested over 24 months. Drug court offenders also averaged fewer total re-arrests than the comparison group (1.25 vs. 1.66). Yet, these results, as well as additional results that isolated drug-related re-arrests, were not statistically significant. (After implementing a time-at-risk adjustment, drug courts did appear to produce fewer re-arrests per year at risk at the .10 significance threshold.)
"A virtually identical percentage of drug court and comparison offenders reported that they experienced at least some incarceration during the 18 months (58 percent vs. 57 percent, n.s.). Drug courts may have reduced the total number of days incarcerated, as the drop from 95.3 days on average for the comparison group to 62.7 days for the drug court sample represents a meaningful 34 percent relative reduction, but the difference was not statistically significant. Additional analyses (not shown in Table 4-4.3) revealed drug court graduation to be a critical intervening factor. Among drug court offenders who had completed their participation by the 18-month mark (n = 630), 27 percent of graduates compared with 93 percent of those failing experienced any incarceration; and graduates averaged only 11.8 days incarcerated, compared with 143.9 days for those failing."

Source

Rossman, Shelli B., et al., "Final Report, Volume 4: The Multi-Site Adult Drug Court Evaluation: The Impact of Drug Courts" (Washington, DC: Urban Institute, June 2011), p. 70.
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