Tuesday, May 24, 2011

Why Can't UCR Use Census Population Figures Like Everyone Else?

The FBI released the preliminary 2010 UCR Crime numbers yesterday. The Preliminary UCR Report just covers the crime number for those cities with a population 100,000 or greater. After I got the press release in my email yesterday morning, I popped on over to the FBI’s Preliminary UCR Report website to take a peek at the numbers.

One thing I noticed about the numbers was something I notice every year, the population numbers they always cite never jive with the US Census population estimates. Up till now I’ve always attributed it to the FBI and Census using a different methodology for projecting the population estimate between the decennial censuses. However, I figured that since the 2010 Census numbers were available that the FBI’s estimate would be recalculated to be more in line with Census. However, when I looked at the numbers for the sleepy little burg where I work, the FBI understated the numbers by about 5,000.

I put together a spreadsheet of the population figures used both by the preliminary 2010 UCR and the 2010 Census numbers. I was surprised that the numbers ranged from a -8.1% under estimate to an 11.74% over estimate just for the Texas cities listed.



Of course the problem with this is that if you take the simple approach to figure crime rates by calculating rate based on the FBI’s population number, these differences can make a big difference in how your rates calculate. One other thing I noticed was that the FBI had 34 Texas cities as having a population of 100,000 or greater. However, comparing this to the 2010 Census numbers, there are only 29 Texas cities with a population like this.

I have never been able to find any note of the source of the population figures that UCR uses. They certainly don’t use the population that we list on the UCR forms we submit because at my agency we always use the US Census estimates. I sure wish that the FBI would get on the same sheet of music as the Census Bureau. After all, they are supposed to be the keeper of the “official” population figures.

2 comments:

  1. Hey there. Wondering the same question, I came across this:

    http://www2.fbi.gov/ucr/ucr_general.html

    If you search for population you can find the description easily. Of course, no explanation of why they do as they do.

    ReplyDelete
  2. Thanks for the comment and the link. Of course looking at how bad they muffed it last year, maybe they will rethink their methodology to get something a little closer to the mark.

    ReplyDelete

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