Clairissa Breen and I presented a paper titled "Targeted Law Enforcement in Camden, New Jersey: Diffusion of Benefits and Displacement of Crime" at the 2007 International Crime Mapping conference. Given that displacement of crime can be a public relations nightmare for police departments, understanding and measure displacement or diffusion of benefits in essential. It seems inevitable that as soon as police target crime in one neighborhood, someone in another neighborhood will be seen on the evening news complaining that all the police are doing is moving crime from that neighborhood into our neighborhood. The weighted displacement quotient compares how much crime occurs between the targeted area (A), the buffer area (B) and the control area (C) before and during the operation to see how crime in those areas has changed. If crime has been displaced into the surrounding buffer or if that surrounding buffer has actually experienced some benefits due to its proximity to the operation, the WDQ will be able to detect that change.
For further information on the WDQ, see: Bowers, K.J. and Johnson , S.D. (2003) 'Measuring the geographical displacement and diffusion of benefit effects of crime prevention activity', Journal of Quantitative Criminology, 19:3, pp. 275-301. I recently added the calculations for the Total Net Effect. For details on that, please see Guerette, R. T. (2009). Analyzing crime displacement and diffusion ( Tool Guide No. 10). Washington DC: Center for Problem Oriented Policing.
Full details of the analytical procedure are available on the 'Analysis details' tab of the spreadsheet.
The Excel spreadsheet available to download here (see link at bottom of the page), calculates the weighted displacement quotient as well as a number of other calculations. All you have to do is feed in the amount of crime in three areas before and during (or after) a police operation. The three areas are a target area, a buffer area, and a control area.
On the first page (shown here) you enter values into the yellow boxes. Stage one asks for crime counts for the target area, a buffer area, and a control area both before and during (or after) the operation. At stage two, you can enter the name of the operation, or if you prefer, the name of the police district or area.
Once you can done that, click the yellow results tab shown at the bottom of the screen. This will take you to the results page where you can print the output and see the result. An example is shown below.
Some things about the spreadsheet:
The SEPTIC program is designed for reasonable numbers. Cells filled with a value of zero will result in a warning on the results page. The statistics used in this program will not function with a zero value in the control area.
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