Linkage analysis in cases of serial burglary: comparing the performance of university students, police professionals, and a logistic regression model

Abstract

University students, police professionals, and a logistic regression model were provided with information on 38 pairs of burglaries, 20% of which were committed by the same offender, in order to examine their ability to accurately identify linked serial burglaries. For each offense pair, the information included: (1) the offense locations as points on a map, (2) the distance (in km) between the two offenses, (3) entry methods, (4) target characteristics, and (5) property stolen. Half of the participants received training informing them that the likelihood of two offenses being committed by the same offender increases as the distance between the offenses decreases. Results showed that students outperformed police professionals, that training increased decision accuracy, and that the logistic regression model achieved the highest rate of success. Potential explanations for these results are presented, focusing primarily on the participants' use of offense information, and their implications are discussed.

Keywords:

• linkage analysis
• comparative case analysis
• serial burglary
• criminal behavior
• decision making

Notes

1. It is difficult to provide an accurate response rate for the professional group given that it is impossible to know how many professionals were reached through our various recruitment postings. However, we can report that 51 packages were sent to police professionals who indicated an interest in taking part in the study. Given that 31 professionals sent back completed packages, the return rate was 60.8%.

2. The fact that a different procedure was used to collect data from the students and professionals could have introduced a number of confounding variables, most of which we believe would favor the police professionals' performances on the linking task. For example, the professionals could have taken more time to complete their packages than the students, and they could have relied more on external sources for assistance (e.g. crime analysis packages). The results of this study, however, do not support this view. As will be discussed in the results section, the students generally outperformed the professionals with respect to linking accuracy.

3. None of the participants in this study were from the jurisdiction where the burglary data originated and, consequently, these participants would not be aware of the base rate unless told about it explicitly.

4. The potential for problems when using self-report measures to determine cue reliance should be noted. There is a relatively large literature, which suggests that people may not have access to their mental processes and, even if they do, they may not be able to articulate anything about those processes (e.g. Nisbett & Wilson, 1977). Thus, the results related to our reliance scores should be treated with an appropriate level of caution.

5. Given that some readers may be more familiar with d' than the AUC, these values will also be provided. As with the AUC, a higher d' value indicates greater linking accuracy.

6. In an attempt to understand why the professionals did not perform as well as the students, in either the untrained or trained condition, the accuracy scores of the various sub-groups comprising the professional group were scrutinized with respect to their background (policing, crime analysis, or other) and location (USA, UK, or Canada). While the small number of judges in each sub-group prevented us from conducting formal significance tests, the accuracy scores for the professionals appear to be low due largely to the relatively poor performance of police officers, particularly in the trained condition. No obvious differences in accuracy scores were found across professionals from different countries, in either the untrained or trained condition.

7. Note that Santtila et al. (2004) also used data from a location that was different from the location where their participants resided and/or worked, but both locations were major cities in Finland (P. Santtila, personal communication, 11 March 2009). It is likely that these cities are much more similar than the various locations relied on in the current study, which consisted of towns and cities from three different countries, with different population densities, road networks, land-use patterns, etc.