1. Psychological Service treatment evaluation studies
The dual roles of the Department of Corrections Psychological Service are to a) reduce recidivism and b) contribute to the safe and humane confinement of offenders. The Psychological Service’s effectiveness is primarily measured by its impact on offender recidivism, an index of only the first role. Psychologists employed by the Department of Corrections Psychological Service deliver cognitive-behavioural offence-focussed interventions to high-risk individuals and groups of offenders.
A series of three evaluation studies have reviewed the effectiveness of the Psychological Service in reducing general recidivism. Each has shown that contact with the Psychological Service reduces the likelihood of recidivism, and that more intensive contact (e.g., treatment completed vs not completed vs assessment only) is associated with a greater reduction in recidivism. The first Psychological Service re-conviction study (Bakker & Riley, 1993) covered the period from 1 July 1990 to 30 June 1991 and followed subjects for up to 2 years (the mean length of time ‘at large’ varied between 402 and 498 days). This study demonstrated a difference of 30 percentage points (effect size of approximately r=+.30) in recidivism for treatment completers (N=235) over the no-treatment control group (N=1727: 37% verses 67% recidivism). Favourable comparisons were also observed between control and other treatment comparison groups (e.g., assessed only, treatment not completed).
The second re-conviction study (Bakker & Riley, 1996) followed the same sample, but over a five year period. In this study additional analyses were undertaken on rate of re-offending and seriousness. This second study noted an erosion of the difference between the recidivism rates of the treatment and control groups from 30 to 22 percentage points. An effect size of r=+.22 nonetheless represents a significant treatment effect particularly given the long follow-up period. In this second study greater attention was also given to accurately matching the control and treatment groups in terms of risk variables (this was not attempted in the first re-conviction study). Using an actuarial risk prediction methodology to control for differences in risk levels between no-treatment and treatment-completed groups further reduced the recidivism difference between the two groups to 12.4 percentage points. Bakker and Riley (1996, p.38) concluded that “This should be seen as a ‘cast iron’ difference in that all possible differences between the groups have been controlled for”. While perhaps somewhat over optimistic in their ability to control for all differences between the two groups, it is certainly evident that all coded offender variables (including risk variables such as age, criminal history, and actuarial risk of recidivism) were robustly matched between the treatment and control groups.
The third re-conviction study (Bakker, 1998) employed the more sophisticated technique of survival analysis to compare various treatment and control groups. Using data obtained between 1 July 1993 and 30 June 1994, a Kaplan-Meier survival curve analyses demonstrated a difference of 12 percentage points between the completed treatment group and a matched no-treatment control group. As with the two previous Psychological Service re-conviction studies, favourable differences were also observed between the control group and the incomplete treatment (6% difference) and assessed only groups (6.5% difference).
In a final sequel to the Psychological Service re-conviction studies, McLean and Grace (1998) completed further analyses on existing data and reported that when all treatment groups were combined (i.e. ‘treatment complete’ and ‘treatment incomplete’ groups combined so as to include drop-outs), and using estimates of survival at 1000 days, an overall effect size for the Psychological Service (on general recidivism) of r=+.14 is obtained. This effect size compares favourably with those reported for international treatment programmes based on established best practice principles. It is also noted that the treatment was equally effective with Māori offenders as with non-Māori offenders.