Another look at across-crime similarity coefficients for use in behavioural linkage analysis: an attempt to replicate Woodhams,Grant, and Price (2007)

Abstract

In the absence of physical evidence, investigators must often rely on offence behaviours when determining whether several crimes are linked to a common offender. A variety of factors can potentially influence the degree to which accurate linking is possible, including the similarity coefficient used to assess across-crime similarity. The current study examines the performance of two similarity coefficients that have recently been compared to one another, Jaccard's coefficient (J) and the taxonomic similarity index (Δ_s), using samples of two crime types, serial homicide (N=237) and serial burglary (N=210). In contrast to previous research, the results indicate that Δ_s does not significantly outperform J with respect to linking accuracy. In addition, both coefficients lead to higher levels of linking accuracy in cases of serial homicide compared to serial burglary. Potential explanations for these findings are presented and their implications are discussed.