An important but often overlooked fact of crime analysis is that crime data changes every year. I don’t mean that crime changes every year, though of course it does. The data itself changes. More specifically, the agencies that report data change. Each year, different police agencies report their data to the FBI.
This means that we can’t simply compare UCR data in 2016 to UCR data from 2015. 2016 has different agencies to 2015 so it isn’t an apples-to-apples comparison.
There has been a lot of talk lately about immigration. In particular, about if immigrants cause crime in the cities they go to. Like a lot of controversial topics, this one is based mainly in anecdotes and exaggerations. Here is some data regarding the issue.
In this post I look at the relationship between crime rates and Mexican immigrant population in 102 counties between 1980 and 2010. For a full methodology and the R code used to analyze the data, see below.