Formal experiments are underused in criminal justice. Disposals matter. Are they effective? And how much do they cost for what they deliver? Good intentions are not evidence of effectiveness.1 2 The same standards of evidence1 3 4 5 6 7 8 9 should apply for judges prescribing a sentence as for doctors prescribing drugs. Given the benefits of good quality research, and the cost of ignoring it, health scientists should advocate for randomised controlled trials in the criminal justice system and confront common objections.

Offenders are also patients, with problems of infection, mental health, and addictions. In dealing with offender patients, judges deserve the same quality of evidence on “what works” as doctors take for granted. There is no methodological or ethical reason why equivalent standards of efficacy and cost effectiveness should not apply in criminal justice. The barriers are cultural and political. Biomedical scientists should raise awareness about the need for formal experiments in sentencing and support their implementation. We should complain about sentencing that is untrialled and not based on evidence, just as we criticise homoeopathic medicine for its lack of an evidence base.

Randomisation for fair comparison was introduced into biological experiments by Ronald Fisher in 1926 and into medicine by Austin Bradford Hill in 1947. Randomised trials in criminal justice date back half a century3 but today exert little influence,3 4 5 10 …