Tuesday, July 10, 2012

60 Steps Revisited: Step 22 – Examine Your Data Distributions

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 the last post in my series covering the book Crime Analysis For Problem Solvers we looked at the necessity to collect our own data. Now that we have the data we need to start our analysis by Step 22 - Examine Your Data Distributions.
I have a confession to make, I never did well in math in school. In fact, if you were to ask my high school math teachers what kind of job I would have as an adult, they definitely would not have guessed one that involves any sort of mathematical competency. Yet, as a crime analyst I spend a lot of time crunching numbers. I like to tell people, I have a calculator with a lot of buttons and I have to use them all.
The authors state:
“After collecting your data you need to know what it is telling you.”
Analysis is the art of learning what the data is telling you. A good way to analyze the data is with statistics. I can hear you all groaning right now. You probably didn’t like statistics when you took it in high school or college. One thing I found is that while I didn’t like math in school because didn’t see the point, now that it can do some very useful stuff and make my life easier, I think it’s pretty neat. What’s even better is that you don’t have to worry about the whole theoretical framework behind how and why statistics work and just concentrate on learning what is useful.
The authors discuss a few basic statistical tools for analyzing data distributions. These tools analyze the average case or the spread of cases. To analyze the average case you can use:
  • Mean
  • Median
  • Mode
To analyze the spread of cases, use:
  • Range
  • Inner Quartile Range
  • Standard Deviation
Another set of tools is used to measure the scale of the distribution. This can be done using:
  • Nominal scales
  • Ordinal scales
  • Ratio scales
I’m not going to try to explain these, but instead will encourage you to hit the link and read them for yourself. Understanding these tools and what they can tell you about your data is really important if you are going to be a problem solving crime analyst. The authors even include a couple of hyperlinks to some websites with additional information about statistics.
Next time we’ll cover Step -23 Diagnose Your Hot Spot.

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