Behavioral Consistency, the Homology Assumption, and the Problems of Induction

The ultimate goal of profiling is to identify the major behavioral and personality characteristics to narrow the suspect pool. Inferences about offender characteristics can be accomplished deductively, based on the analysis of discrete offender behaviors established within a particular case. They can also be accomplished inductively, involving prediction based on abstract offender averages from group data (these methods were detailed extensively in Chapter 2; see also Petherick & Turvey, 2008a). As discussed, these two approaches are by no means equal. The reliability and validity of inductive profiling rest almost exclusively on two essentially weak theories: behavioral consistency and the homology assumption. Behavioral consistency posits that the same offender will do the same thing across the span of time during different offenses. The homology assumption suggests that, generally, there will be a similarity between different offenders who commit similar crimes. Without the ability to utilize either of these theories, comparing the current offender( s) to past offenders is essentially futile. ... This chapter provides an in-depth discussion of both behavioral consistency and the homology assumption, outlining some of the research that has been done in the area. The purpose is to educate students and professionals regarding what these concepts are, why they are important, and the consequences to casework in light of their limitations. It builds on the discussion of inductive methods presented in Chapter 2.