A line in the stats: gerrymandered crime reporting

This weekend, the Ann Arbor News offered a look “behind the numbers” at crime stats in the Ypsilanti area.  Their findings: crime is higher than state and national averages in the City of Ypsilanti, near or below averages in Superior Township and Ypsilanti Township.

Unfortunately, the story spends a lot of ink on the numbers itself–not necessarily a bad thing–with virtually no “behind” to be found.  The analysis of why a disparity might exist is limited to a vague quote from a city police officer that sums up to “I don’t know,”

Ypsilanti police Lt. Deric Gress attributed the higher crime rates to Ypsilanti’s urban nature, with an estimated 19,809 people living in four square miles, per the U.S. Census. “I don’t have a real reason we’d be higher than any others, other than being in an urban environment,” he said.

and some discussion of differential levels of community engagement, a discussion that uses a few anecdotes of positive engagement in areas like West Willow to generalize across the township, while generalizing that the city police have struggled in recent cases with a prevalent ‘No Snitching’ culture in the city.” This discussion ignores that the city’s police department started a community policing program like the one lauded in West Willow a decade ago, and the “uncooperative witness” factor, as far as I can tell, has been limited to a few shootings at a single housing complex.  (But it makes a good story, right?)

Coming up with some theories on the “why” behind the numbers isn’t that hard; here’s a couple, with some discussion:

  1. Ypsilanti is a college town.  College kids do dumb stuff, with some of that stuff being criminal and some of it leading to them being victims of crime. Consider these two graphs, the first from the City of Ypsilanti’s Master Plan, the second from the Bureau of Justice Statistics’ Arrest Data Analysis Tool (This is a thing.  Cool!)

    College town Ypsi has nearly 3 times the 18- to 24-year-olds of Ypsi Township or Michigan--an age bracket featuring prominently in Federal arrest statistics.
    College town Ypsi has nearly 3 times the 18- to 24-year-olds of Ypsi Township or Michigan–an age bracket featuring prominently in Federal arrest statistics.
  2. Ypsilanti has a lot of people living in poverty. Poverty exposes people to crime as well as making crime appealing, for lack of access to better opportunities.  As of the 2012 ACS, 28.8% of Ypsi City residents were living in poverty, compared to 16.3% of Michigan residents.  A quick literature search finds a 2011 paper from Justice Policy Journal, Does Age or Poverty Level Best Predict Criminal Arrest and Homicide Rates? A Preliminary Investigation, which finds that, “poverty … displays three to four times
    more explanatory power in predicting arrest rates and eight times more in predicting homicide death rates than does age”. (That is, teenagers are more likely to live in poverty than 40-year-olds, and it is their poverty, not their age, that is the best statistical predictor of their being arrested or murdered.)  I especially like this link for contradicting my first theory, leaving some work for the enterprising journalist!

There are policy implications of each of these hypothesis that we could dive into (and should! …in a future post), but the one I want to call attention to up front is Sheriff Clayton’s slicing and caveating of the data:

After Washtenaw County Sheriff Jerry Clayton’s statements in July that the crime rate in eastern Washtenaw County is below the national and state crime rates, The Ann Arbor News analyzed crime rate statistics from 2008 to 2012 — the last five years available — from Ypsilanti, Ypsilanti Township and Superior Township, the three most populated areas of eastern Washtenaw County. …

On Thursday, Clayton clarified his statement, saying he was speaking about the areas the sheriff’s office is primarily responsible for, Ypsilanti and Superior townships.

“If you add in the city’s numbers, that’s what spikes it and when I’m talking (in the press conference), I’m talking about our area,” Clayton said. “When you take Superior and Ypsilanti Township, they are below the national rate.”

This whole “investigation” was sparked by a comment of Clayton’s, in which he has to draw a particular line–adding Superior Township to Ypsilanti Township, but carefully excluding the city that’s directly in the middle of that area–to bring his stats down below a target number. He’s not slicing by political jurisdiction, lest Ypsi Township look bad, nor by “community” in an identity sense of the word, because he’d have to include the city, but by what makes the numbers line up in his department’s favor.

If the standard by which we’re measuring crime prevention is how well somebody can draw creative lines to make the crime Somebody Else’s Problem, then we stand little chance of actually addressing it.

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About Me

Michigander, parent of twins, urban planner, role-playing game nerd.


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