What is a ‘good enough’ prison? An empirical analysis of key thresholds using prison moral quality data 1

Performance thresholds and minimum standards in prison have preoccupied policy makers and practitioners alike for some time. These standards are based on widely accepted statements of principle, but benchmarks are rarely set or explored empirically. Nor has there been any attempt to describe or define higher-end thresholds; the point at which outcomes become positive, or stated principles are achieved. In this study, we provide an empirical demonstration of how quality of life thresholds may be determined using data from 518 Measuring the Quality of Prison Life (MQPL) surveys conducted in prisons in England and Wales (2009–2020) and examine their relationship to five violence outcomes: serious prisoner on prisoner assaults, serious assaults on staff, self-harm incidents requiring hospital treatment, self-inflicted deaths, and homicides. The results suggested that thresholds exist for most of the MQPL dimensions. A set of lower ‘unsafe’ and higher ‘minimally safe’ thresholds were produced. We found that the scores of prisons below the lower threshold had a very strong relationship with each of our five serious forms of violence in prison. Similarly, prisons that did not manage to cross the ‘minimally safe’ threshold also had strong relationships with incidents of violence in their prison but were at slightly lower risk of those incidents occurring. Striking differences in mean incidents rates were found when comparing prisons below the lower threshold to prisons above the ‘minimally safe’ threshold. Our findings suggest that to operate a safe enough (and therefore legitimate) prison, a combination of harmony, security and professionalism dimensions above a certain threshold should be achieved.