How Concentrated is Crime at Places?


 
    There is increasing awareness about the importance of crime concentration at places.  But scholars have not systematically reviewed the sizeable body of research on crime concentration at places. Lee et al. conducted a systematic review of literature pertaining to crime concentration at place from 1970 to 2015.  Their objective was to determine the consistency of findings from these studies.   In this study, Lee et al. found 44 studies that empirically investigate crime concentration at places and had sufficient information to measure crime concentration at places. 
 
    Lee et al. examine crime concentration at places in terms of prevalence (all places are studied) and frequency (only places with at least one crime are studied). In the prevalence studies, the top 10% of serious crime places account for 63% of crime, while the top 10% in the frequency curve account for 43% of crime. The difference in concentration is mostly due to the fact that most places do not have crime. 
 
    The study also compared concentration by different measures of crime. Many studies use calls for service data to measure crime. Others use crime incident data to measure crime. Calls for service are more concentrated at places than crime incidents. This is true for both the frequency and prevalence studies. This finding suggests that research using calls for service as a proxy for crime may be inflate crime concentration.  Further, calls for service may include various non-crime events. 
 
    A place can be an address, household, street segment, or an area. As the size of the place being studied decreases, crime becomes more concentrated. In terms of prevalence, the most crime afflicted 5% of addresses account for 55% of crime, the worst 5% of street segments account for 42% of crime, and the worst 5% of neighborhoods account for 20% of crime. In terms of frequency, households display the least concentration, and addresses the most, with street segments falling in between. Given a first crime, addresses have a higher chance of a second or third crime than do street segments or households. This may have to do with the heterogeneity of addresses relative to households. Addresses can be businesses or all types of places, which are more at risk of crime and repeat victimization than households. 
 
    Lee et al. also examine the change in concentration of crime over time, comparing three periods. One before the crime drop of the 1990s, one during, and one after. The prevalence curves show less concentration in the “after” period than the other two time periods. This suggests during the 1990s, both crime and crime concentration at places dropped. In terms of frequency, crime is more dispersed across different places, and did not change among places after 1999.  This suggests that the 1990s crime drop influenced the chances of a place being a site of crime more than the chance of a new crime after an initial crime.  
 
    Lee et al. also examined concentration of crime across U.S. and non-U.S. countries. The prevalence studies show that crime is more concentrated at a smaller proportion of places in the U.S. The worst 10% of places in the U.S. account for 70% of crime whereas the worst 10% of places outside the U.S. account for 58% of crime. The frequency studies shows no substantial difference in crime concentration between U.S. and non-U.S. countries. Though the U.S. data are from a single country, their variation is greater than data from outside the U.S.  This suggests that cities and counties in the U.S. have very different experiences with crime concentration at places. 
 
    Finally, Lee et al. examined concentrations for violent and property crime. In terms of prevalence, the top 10% of places account for 60% of violent crime and over 70% of property crime. There are many fewer violent crimes than property crimes, so this is an unusual finding. Unfortunately, the frequency curves revealed no significant differences in concentration of violent and property crimes. The authors cannot resolve this issue within the scope of their study. 
 
    Overall, the study finds that crime is concentrated at a relatively small number of places regardless of the way crime is measured, the geographic unit used, or type of crime. The amount of concentration, however, varies due to measurement, unit of analysis, and crime type differences. Crime concentration also varies depending on whether one is measuring prevalence or frequency.  
 

Takeaway: 
  • Crime is concentrated at a relatively small number of places. 
  • The smaller the size of the place, the more concentration.
  • The amount of crime concentration varies based on how crime is measured and crime type.
 

Reference: 
Lee, Y., Eck, J., O, S., & Martinez, N. (2017). How concentrated is crime at places? A systematic review from 1970 to 2015. Crime Science, 6(1), 1–16. https://doi.org/10.1186/s40163-017-0069-x