Center for Problem-Oriented Policing

Appendix C: Use and Interpretation of Coefficients to Measure Displacement and Diffusion

Coefficient Use Interpretation
Gross Effect (GE) Determines increase or decrease in response area. Positive number > 0) indicates decrease in crime; Negative number < 0) indicates increase in crime. Zero = 0) means there was no change.
Net Effect (NE) Determines increase or decrease in response area in relation to changes in control area. Positive number > 0) indicates decrease in crime; Negative number < 0) indicates increase in crime. Zero = 0) means there was no change.
Weighted Displacement Quotient (WDQ) Determines the extent of displacement or diffusion in buffer areas in relation to changes in response and control area.   Positive number > 0) indicates there was a diffusion effect and any response effects were amplified; If number is greater than positive one > + 1.00) then the diffusion effect was greater than the response effect. Negative number < 0) indicates there was displacement. A negative number between zero and negative one < 0 > -1.00) means the displacement was not greater than the response effects and the intervention still achieved some benefit. A negative number beyond negative one < -1.00) means the response effect was eclipsed or erased by displacement. Zero = 0) means there was no effect.
Success Measure Determines the degree to which the decrease in the action area outweighs that in the control area (i.e., the degree to which the response was successful). Negative number < 0) indicates successful responses where the decrease in the action area outweighed that in the control area. Positive number > 0) indicates responses where the response was not effective.
Buffer Displacement Measure Determines whether the interventions show possible evidence of displacement or diffusion. Positive number > 0) indicates a possible displacement effect. Negative number <0) indicates a possible diffusion of benefit.
Total Net Effect (TNE) Determines the overall effect of the response in relation to changes in the control area while adjusting for displacement and/or diffusion effects. Positive number > 0) indicates response was effective overall; Negative number < 0) indicates it was not. Zero = 0) means there was no change. The greater the number, either positive or negative, the more or less effective the response, respectively.