||Crime is a serious business. It causes great distress and fear. It costs a lot
to deal with its consequences. In these regards crime shares much with
the problem of ill-health and disease. The application of sound science and
statistics has allowed great strides to be made in dealing with problems of
ill health. Medical statistics is one of the recognised, established
disciplines involved in researching healthcare.
The parallels between research in crime reduction and in healthcare do
appear to differ in terms of quality. Although there is still room for
considerable improvement in researching health-care, an investigation
into the underpinning of statistical methods used indicates that the
problems are substantially worse in the study of crime. The consideration
given to statistics in crime studies seems rather flimsy, yet important
claims are made which are statistical at source and may affect policy, and
so can have considerable costs attached. Therefore, for example, it is
important to know whether the underlying crime level has really changed,
rather than just being the result of perhaps sampling variation or some
artefact giving rise to statistical bias or systematic error. This is necessary
when trying to determine whether a Crime Reduction Intervention (CRI)
has actually worked.
I started examining the scientific basis of the claim for the effectiveness for
one particular CRI, basically because I was concerned about negative side
effects and I thought the claim implausible. I remain concerned and
unconvinced. The statistical issues and concerns I raise apply also to
investigating other CRIs and to existing published analyses.
This piece extends work presented in Marchant (2006); earlier work on the
statistical issues involved can be found in Marchant (2005a, b; 2004).