Information on the pilot study designed to cut reconvictions at Peterborough Prison has dribbled out in an unsatisfactory way. But with the publication of a report by RAND Europe at the end of May we now know a little more than we did – though by no means enough – about how this flagship project will be run.
The report, called Lessons Learned from the planning and early implementation of the Social Impact Bond at HMP Peterborough, is based on interviews with 22 insiders who have been involved with setting up the scheme. Social Finance raised £5 million from investors to fund the bond: they will get a return on their investment if reconviction rates at Peterborough are lower by a defined amount than those of a control group of prisoners released from other prisons.
The scheme aims to reduce reconvictions in the 18 months after release for offences committed in first year post-release for 3,000 consecutive short-sentence (up to 1 year) prisoners liberated from HMP Peterborough in 5+ years from September 2010. Crucially, short-sentence HMP Peterborough prisoners liberated from court are ineligible.
Three cohorts, each of 1,000 ex-prisoners, allows for interim analyses and early pay out to SF investors if at least a 10 per cent reduction in reconvictions is observed per cohort. Commendably, cohort-size was determined for statistical assurance on the precision of the estimated reduction. SF investors will get a return if the services, delivered to prisoners both before and after release, succeed in reducing reconvictions by 10 per cent (or more) per cohort of 1,000 eligible ex-prisoners compared to controls; or by 7.5 per cent (or more) across all 3,000 eligible ex-prisoners. A cap has been set so that MOJ’s total pay-out is limited in the event that One Service (as the service is called) delivers more than anticipated.
The cap is not spelled out in the RAND Europe report but earlier disclosures about the scheme suggest that it has been set at £13 million. (In 2010 money? This is not clear.) The authors do disclose that MOJ’s provision on how much it is likely to have to pay out is off the Treasury books – an uncanny characteristic of government private finance initiatives that Professor Allyson Pollock has lambasted in the NHS. This lack of transparency is a key statistical issue because the amount of prior provision derives directly from the prior plausibility (or probability) that MOJ attaches to each percentage point of reduction in number of reconvictions. Bayesians beware!
Selecting controls against which the released Peterborough prisoners willhttp://www.blogger.com/img/blank.gif be compared is a key issue. Here lie the greatest weaknesses of the pilot.
Randomizing eligible offenders within HMP Peterborough – some to One Service, others as controls - was rejected as an interference with SF’s business model, which relies on maximizing the number of ex-prisoners released into the local area in which SF’s partners operate the services delivered after release. Randomization would have reduced their case-cohort by half (50:50 randomization) or a third (67:33 randomization) but bolstered the evidence-base.
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