Although they seem to identify low-risk individuals with high levels of accuracy, the authors say “their use as sole determinants of detention, sentencing, and release is not supported by the current evidence”.
Risk assessment tools are widely used in psychiatric hospitals and criminal justice systems around the world to help predict violent behaviour and inform sentencing and release decisions. Yet their predictive accuracy remains uncertain and expert opinion is divided.
An international research team, led by Dr Seena Fazel at the University of Oxford, set out to investigate the predictive validity of tools commonly used to assess the risk of violent, sexual and criminal behaviour.
They conducted a large-scale analysis of 68 independent studies comprising risk assessments of 24 827 people from 13 countries, including the UK and the USA. When analysing the results, the team took into account differences in study quality to identify and minimise bias.
Overall, 24 per cent of the studies’ participants (5879) committed an offence over an average of 50 months. High rates of false positives were wrongly identified as being at high risk of repeat offending.
The results also reveal that the risk assessment tools assessed had a predictive accuracy similar to chance levels when identifying those at most risk of committing a crime. For example, only 41 per cent of individuals judged to be at moderate or high risk by violence risk assessment tools went on to violently offend, and 23 per cent of those judged to be at moderate or high risk using sexual risk assessment tools went on to sexually offend.
Of those judged to be at moderate or high risk of committing any offence, just over half (52 per cent) did. However, of those predicted not to violently offend, 91 per cent did not, suggesting that these tools are more effective at screening out individuals at low risk of future offending than predicting those that are most likely to commit a crime. The predictive accuracy of the tests did not seem to be affected by factors such as gender, ethnicity, age or type of tool used.
Although risk assessment tools are widely used in clinical and criminal justice settings, their predictive accuracy varies depending on how they are used, say the authors.
Dr Fazel, a Wellcome Trust Senior Research Fellow in Clinical Science, said: “Our review would suggest that risk assessment tools, in their current form, can only be used to roughly classify individuals at the group level, not to safely determine criminal prognosis in an individual case. The extent to which these instruments improve clinical outcomes and reduce repeat offending needs further research.”
Image: Angry face. Credit: teapics on Flickr.
Fazel S et al. Use of risk assessment instruments to predict violence and antisocial behaviour in 73 samples involving 24,827 people: systematic review and meta-analysis. BMJ 2012 (epub ahead of print).