Prospective crime mapping in operational context Final report

time course of repeat victimisation (RV). Research consistently demonstrates that when RVoccurs it does so swiftly offering a limited but precise window of opportunity for intervention(e.g. Polvi et al., 1991). Risk is unstable. Thus, repeat victimisation may be said to be aspecial case of space-time clustering, events tending to occur swiftly at the same locations.Inspired by the precepts of optimal foraging theory, the authors have recently examinedwhether RV is part of a more general foraging pattern (Johnson and Bowers, 2004a). Thetheory, borrowed from behavioural ecology, is that when searching for resources, offenderswill aim to limit the time spent searching for suitable targets, whilst simultaneously seeking tomaximise the rewards acquired thereby minimising the associated risks. RV is arguably anexample of optimal foraging. A conjecture from Farrell et al. (1995) illustrates this. Farrell etal. suggest that:“a burglar walking down a street where he has never burgled before sees two kinds ofhouse – those presumed suitable and those presumed unsuitable. (The latteridentified by dint of an alarm, by occupancy, the presence of a barking dog, and soon). He burgles one of the houses he presumes suitable, and he is successful. Nexttime he walks down the street, he sees three kinds of house – the presumedunsuitable, the presumed suitable, and the known suitable. It would involve the leasteffort to burgle the house known to be suitable.”Farrell et al. (1995)Thus, offenders target those properties with which they are most familiar, and which combinegood rewards and acceptable risks. A natural extension of this strategy would be to target notonly those previously burgled and known to be suitable but also those houses that are mostsimilar to them, in terms of the likely risks and rewards and the effort involved in burglingthem. The first law of geography states that things which are closest to each other in spaceare the most similar. It follows that homes nearest to burgled houses may represent the nextbesttargets. For this reason, using data for the county of Merseyside and methodsdeveloped in the field of epidemiology (Knox, 1964), the authors conducted a series of studiesto examine whether the risk of burglary clusters in space and time more generally. That is,does the risk of burglary appear to be communicated from one property to another in muchthe same way as the behaviour of a disease? 1A series of confirmatory findings followed. In particular, for the area studied, the researchdemonstrated that the risk of burglary was communicated over a distance of about 400m andthis elevated risk endured for around one month (Johnson and Bowers, 2004a), after which itappeared to move to other nearby areas (Johnson and Bowers, 2004b). Additionally, adisproportionate increase in risk for those on the same side of the street as the burgled homewas evident. The communicability of risk varied by area, with risk appearing to be mostcommunicable in the most affluent of areas (Bowers and Johnson, 2005a), though somedegree of communicability was well-nigh universal.The practical implications of this programme of research are clear: crime reductive actionshould be directed towards the burgled home, and also to those nearby. However, oneconcern raised was the practicability of implementing such a strategy on a large scale.Consider that the implementation of a strategy for which every burgled household andneighbours within 400m received crime reduction attention would require substantialresources if implemented across an area such as a police Basic Command Unit. For obviousreasons, such a strategy is unlikely to generate much enthusiasm.What is required is a more precise method of generating reliably accurate predictions ofwhere crime will most likely next occur. Such a method should enable the efficientdeployment of resources. The rough location of a high concentration of crime could easily bepredicted by simply identifying a large urban area, but this would be of little operational value.The challenge, then, is to identify where a high concentration of crime will occur for arelatively small area. Considering the findings in relation to crime concentration, for an1 The authors do not suggest that burglary exudes a bacillus but that the clustering of events in space and time mightsuggest that it does so.2