Reviews of Offender Rehabilitation
In the years since Martinson’s original publication the pendulum has firmly swung back in favour of the notion that corrections based treatment can influence an offender’s behaviour in prosocial directions. Indeed, a substantial and robust body of empirical research is now available to support the effectiveness of some interventions for offenders. Most significantly, a large number of meta-analytical 1 studies attest to the efficacy of some correctional treatment approaches (Andrews, 1995; Andrews, Zinger, Hoge, Gendreau, & Cullen, 1990; Dowden & Andrews, 1999, 2000; Garrett, 1985; Izzo & Ross, 1990; Lipsey, 1992; Lipsey, Chapman & Landenberger, 2001; Lipton, 1994; McGuire & Priestley, 1995; Wexler, Falkin & Lipton, 1990; Whitehead & Lab, 1989).
While it is beyond the scope of the current article to review all of these meta-analyses, a number of recent attempts have been made to ‘review the reviews’. For example, Losel (1995) reviewed twelve meta-analyses on correctional treatment. He reported that effect sizes ranged between r=+.05 and r=+.36, with an estimated mean effect for all assessed studies of r=+.10. Since Losel’s 1995 review, McGuire (2000) has identified a further six meta-analyses. In combining the 18 meta-analytic reviews published between 1985 and 2000, McGuire reports a mean reduction in recidivism of between 5 and 10%. However, most importantly, he further identifies that many individual studies, and even some meta-analyses, report effect sizes considerably larger than this. This suggests that some methods of correctional intervention are consistently more effective at reducing recidivism than others. It is upon this basis that the New Zealand Department of Corrections has embarked on a policy of designing, implementing and evaluating its rehabilitative programmes in accordance with what is internationally regarded as ‘best practice’. Best practice in correctional programming entails the application of a structured cognitive-behavioural approach that focuses on addressing risk factors for criminal recidivism (Andrews, 2001; McGuire, 2002). The ultimate goal for the New Zealand Department of Corrections is to improve the cost effectiveness of programmes, and to maximise the rehabilitative potential, in terms of reducing recidivism, of correctional programmes.
1 Meta-analytic techniques are popular in outcome research as they allow for the statistical aggregation of results from independent studies (Garrett, 1985). The key outcome variable in meta-analysis is the mean effect size (r). An effect size provides an estimation of the difference in recidivism rates between experimental and control samples. For example, an effect size of r=+.10 would equate to a difference of 10 percentage points between the experimental and control group. Thus, if the recidivism rate for the control group was 55%, an effect size of r=+.10 would translate to a reduction in recidivism from 55% to 45% for the experimental group.