|Title||Peterborough social impact bond: final report on cohort 2 analysis|
|Authors||Anders, J. and Dorsett, R.|
In 2010, the world’s first Social Impact Bond (SIB) was launched at Peterborough Prison. It was used to fund an intervention – ‘The One Service’ – aimed at reducing the reoffending among prisoners discharged after serving a sentence of less than 12 months. Under the terms of the SIB, investors are paid according to how successful the One Service is in reducing reconvictions. If a minimum threshold of a 7.5% reduction in reconviction events is reached across the pilot, payment is triggered. Additionally, there is an option to trigger an early payment if a 10% reduction is noted in the number of reconviction events in individual cohorts.
A propensity score matching (PSM) approach was used to estimate impact. For cohort 1, the impact was estimated, by a previous team of independent assessors, to be a reduction in reconviction events of 8.4% (Jolliffe and Hedderman, 2014). Anders and Dorsett (2017) reviewed the PSM approach, prompted in part by the desire to understand the reasons behind the differences in reconviction rates between prisoners discharged from HMP Peterborough and prisoners discharged from other prisons. Following their review, Anders and Dorsett (2017) recommended that the cohort 1 approach be maintained for cohort 2. They also recommended an adjustment to the sample selection in Cohort 2. It is important to note that this recommendation was based on the analysis of cohort 1 data and was not informed by cohort 2 reoffending data. Matching was performed for cohort 2 using a dataset that excluded reoffending data.
We estimate that the One Service reduced the number of reconviction events among those discharged from HMP Peterborough by 9.7% for cohort 2. The reduction across both cohorts is estimated to be 9.0%, which reached the minimum threshold of 7.5% across all cohorts. This reduction is sufficient to trigger an outcome payment.
|Publisher||Ministry of Justice|
|Published||27 Jul 2017|
|Web address (URL)||https://www.gov.uk/government/publications/final-results-for-cohort-2-of-the-social-impact-bond-payment-by-results-pilot-at-hmp-peterborough|