Thursday, September 13, 2012

60 Steps Revisited: Step 47 – Know How To Use Controls

Back in 2009, I did a series of posts covering the excellent book Crime Analysis For Problem Solvers. The book is published by the US DOJ's Problem Oriented Policing Center (POP Center). Because of the value I think this book has for crime analysts, and policing in general, I am going to re-post this series on here on the blog.

In this chapter in our walk through the book Crime Analysis For Problem Solvers we’re going to look at Step 47 – Know How To Use Controls. When we talk about controls here, we aren’t talking about knobs and buttons, we’re talking about using control groups.

A control group is a way to determine if your problem solving strategy is working. In other words, a scientist working on a new medicine may  give the medicine to one group of lab rats and a placebo to the control group. If the level of sickness in control group is not markedly different than the group that got the medicine, then this experimental medicine may not be working.

In a similar way using controls can help you determine if your response to a problem is working, not working or something else is at work if your problem changes.

There are a number of things that can cause changes in your problem that isn’t related to your response. Some of them are:
  • Cycles of activity
  • Long term trends
  • Unexpected events
For example, in the sleepy little burg where I work, we always see a slow down in crime during the winter months. This is a normal cycle of activity. If we implement a response to a crime problem right before the winter months, any decrease may have little to do with the effectiveness of our program.  Using a control would help us to ensure that any change was due to our efforts and not just coincidence.
Next time we’ll cover Step 48 – Consider Geographical And Temporal Displacement.

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