Do stickers indicating the use of forensic property marking prevent burglary? Results from a randomized controlled trial

Abstract

This paper examines whether the posting of sticker decals indicating the use of forensic property marking deters burglary. The study is a randomized controlled trial (RCT). The sampling frame includes all (N = 6603) single-family houses in the municipality of Aarhus, Denmark, that were burgled once or more during the 4 years prior to the experiment. Houses were randomly assigned to treatment (n = 3378) and control (n = 3225). Treatment houses were offered a free forensic property marking kit and asked to post sticker decals around their front doors indicting their use of the product. Control households were not contacted. A process evaluation determined that only one-third (n = 1080) of the houses assigned to treatment requested property marking kits and posted stickers as instructed. An intention-to-treat (ITT) effect analysis was based on the full treatment group despite a low (32%) compliance rate. At the end of a 15½-month observation period, the full treatment group had experienced 21% fewer burglaries than the control group – a difference that is both substantively and statistically significant (χ2 = 5.305, p = 0.021 n = 6608). Analysis revealed that the preventive effect was limited to the beginning of the observation period and declined thereafter. It is therefore possible that some of the overall result may have been due to an “availability effect,” i.e., a heightened vigilance induced by the initial contact letter. The preventive effect of treatment seems incontestable. This said, the full pattern of results suggests that the reduction in burglary was likely due to a combination of treatment and availability effects.