Predicting Domestic Homicides and Serious Violence in Dorset: a Replication of Thornton\u2019s Thames Valley Analysis

Abstract

Research QuestionWhat facts known to police, if any, could have predicted the 107 domestic and family murders and near-murders in Dorset (UK) police area over a recent 7-year period, using methods identical to Thornton’s (2011, 2017)?DataThe data were gathered from all 107 cases of domestic murders, manslaughter, attempted murder or grievous bodily harm with intent in Dorset between April 2009 and March 2015, plus a matched control sample of 214 arrestees for less-deadly violent offences.MethodsReplicating Thornton’s Thames Valley analysis, two methods were used: (1) calculating errors in predictions from previous risk assessments using the UK’s DASH (Domestic Abuse, Stalking and Harassment) risk assessment protocol and (2) making a case-control comparison of Thornton’s risk factors between the deadly domestic violence cases in Dorset to a Dorset sample of victims and offenders in all violence cases during the same time period.FindingsFalse negative risk assessments were found in 67% of the deadly violence cases with prior police contact (45 of 67) not classified by DASH as ‘high risk.’ The false positives in the same time period totalled 12,279 cases of no serious harm among 12,301 cases receiving high risk assessments, for a 99% false positive rate. Possible alternative predictors were found in differences between deadly offenders and controls, both male and female, although it is not known whether these variables were added to the records before or after the deadly violence event. Male offenders in deadly violence cases were 120% more likely to have their police records note a self-harm warning, 20% more likely to have a suicide warning, yet only half as likely to have a mental health warning as control males. Female offenders in deadly violence cases were 355% more likely to have a weapons warning on file, 244% more likely to have a mental health warning and 146% more likely to have a drugs warning than female control case offenders.ConclusionsThe current risk assessment tool (DASH) failed to predict the majority of deadly domestic violence cases over 6 years in Dorset. Other factors could do better, but more research is required before highly accurate forecasting tools can be applied to help save the lives of more domestic abuse victims.