For quite a while now I have been walking through the excellent book Crime Analysis For Problem Solvers one step at a time. In this post, we'll cover Step 18 - Learn If The 80 - 20 Rule Applies. While I have been summarizing and commenting on this book, it should in no way substitute you, as a crime analyst, actually reading the whole book. You can read it on the web, download a PDF copy or even order a printed version. There are so many good things in this book that it's worth keeping a dead trees version in your office.
The authors describe the 80-20 rule as:
This phenomenon is commonly called the 80-20 rule, where in theory 20 percent of some things are responsible for 80 percent of the outcomes. In practice, it is seldom exactly 80-20, but it is always a small percentage of something or some group involved in a large percentage of some result. Source: Crime Analysis For Problem SolversThey also quote a number of crime studies that found similar results. Many in law enforcement have similar anecdotal accounts of a small number of prolific offenders being responsible for a large number of offenses. We see this when we clear a large number of cases by arresting one or two offenders.
None of us have an unlimited number of resources to fight crime, or at least no law enforcement agency that I am aware of does. (However, if you work for an agency with an unlimited number of resources, let me know so I can send you my resume.) With a limited number of resources, we should use those resources where they will have the greatest effect. Applying the 80-20 rule to this, if we can identify the small number of causes that have the greatest number of outcomes and then apply our limited resources to them we will have the greatest effect.
As an example, the authors point to an analysis of construction burglaries in Jacksonville, Florida. In their analysis it was determined that only 20 percent of the builders were victims of 85% of thefts and burglaries. If your analysis of problems in your city uncovers a similar disparity, it should cause you to look for the reason they are such a prolific victim. If you can get the victim to modify the behavior that makes them such an easy target you can have a significant impact on the number of crimes reported. As any police chief will tell you, lower crime numbers are always good.
Next time we'll look at Step 19 - Research Your Problem.