5 Things About Crime Statistics

Commenter Bluecat57 passed along an article a few weeks ago about the nightclub shooting in Thousand Oaks, California. Prior to the tragedy, Thousand Oaks had been rated the third safest city in the US, and it quickly lost that designation after the shooting. He raised the issue of crime statistics and how a city could be deemed “safe”. This seemed like a decent question to look in to, so I thought I’d round up a few interesting debates that crime statistics have turned up over the years.

Ready? Here we go!

  1. There’s no national definition for some crimes In this age of hyperconnectedness, we tend to all assume that having cities report crime is a lot like reporting your taxes or something. Unfortunately, that’s not the case. Participation in most national crime databases is voluntary, and every jurisdiction has their own way of counting things. For example, 538 reported that in New York City, people who were hit by glass from a gunshot weren’t counted as victims of a shooting, but other jurisdictions do count them as such. Thus, any city that reports those as shootings will always look like they have a higher rate of crime than those that don’t.
  2. Data is self-reported by cities and states Self reporting of anything can be known to influence the rates, and crime is no exception. One doesn’t have to look hard to find stories of cities changing how they classify crimes in response to public pressure. Even when everyone’s trying to be honest though, self-reports can be prone to typos and other issues. That’s why earlier this year NPR found that national school shooting numbers appear to have been skewed upward by reporting mistakes made by districts in Cleveland and California. One way of catching these issues is to ask people themselves how often they’ve been victimized and to compare it to the official reported statistics, but this can lead to other problems….
  3. Crimes are self-reported by people For all crimes other than murder (most of the time) police can’t do much if they don’t know about a crime. Some crimes are underreported because people are embarrassed (falling for scams comes to mind), but some are underreported for other reasons. In some places, people don’t believe  the police will help, that they will make things worse, or that they won’t respond quickly, so they will not report. Unauthorized immigrants frequently will not call the police for crimes committed against them, and some studies show that when their legal status changes their crime reporting rate triples. Additionally, crimes are typically not reported when the others involved were also committing crimes. Gang members will probably not report assault, and sex workers likely won’t report being robbed.
  4. Denominators fluctuate One of the more interesting ideas Bluecat57 brought up when he passed the article on to me is that some cities suffer from having changing populations. For example, cities with a lot of tourists will get all of the crimes committed against the tourists, but the tourists will not be counted in their denominator. In Boston, the city population fluctuates by 250,000 people when the colleges are in session, but I’m not clear what population is used for crime reporting. Interestingly, this is the same reason we see states like Hawaii and Nevada reporting the highest marriage rates in the country…they get tourist weddings without keeping the tourists.
  5. Unusual events can throw everything off Getting back to the original article that sparked this whole discussion, it’s hard to calculate crime rates when there’s one big event in the data. For example, people have struggled with whether or not to include 9/11 in NYCs homicide data. Some have, some haven’t. It depends on what your goal is, really. For a shooting like the one in Thousand Oaks, this would put them well ahead of the national average for this year (around 5 murders per 100,000 people) at 9 per 100,000, and immediately on par with cities like Tampa, FL. A big event in a small population can do that.

So overall, some interesting things to keep in mind when you read these things. As a report in Vox a few years ago said “In order for statistics to be reliable, they need to be collected for the purpose of reliability. In the meantime, the best that the public can do is to acknowledge the problems with the data we have, but use it as a reference anyway.” In other words, caveat emptor, caveats galore.


5 thoughts on “5 Things About Crime Statistics

  1. Homicide is a solid statistic for measuring violent crime because there needs to be a body. You’ve got one or you don’t. Robbery, rape, assault – all those can be underreported or overreported. Yet even that has problems over time. We can save more people with better emergency medical techniques now, so some are downgraded to attempted murders or assaults.


  2. Many years ago,when I was living in Philadelphia, that city led the nation in car thefts by a big margin. The reason was that it was described as “driving without the consent of the owner” or some such thing, so was legally not considered a felony. This made the Philadelphia crime statistics look good, but was terrible for the citizens because penalties for car theft were so low that there was very little disincentive to steal cars.

    Now, I live in a small-to-medium sized city. It is pretty safe place, the kind of place where people still leave their homes and cars unlocked. However, statistically the murder rate is high. But, if you look at the individual killings, it seems to often be some guy from Cleveland shooting another guy from Detroit. As it happens, we are at the intersection of three interstates, so a lot of drugs flow through the city, and many of the killings are related to drug deals gone bad, not robberies or random shootings. Most residents are not affected, but the statistics look bad.


    • @ Uncle Bill – Center Ossipee, NH has an unusual number of criminals for a very small town (561), for very similar reasons. If you look at it on a map, you can see it is an ideal transfer point for drugs coming up out of Boston and the North Shore to be divided and sent to Lakes Region, Northern NH, and Central Maine. Which it is. (Coatal Maine’s drugs come up the seacoast.)

      You’d think having Carroll County House of Corrections there would give people pause. It doesn’t. We get an exorbitant number of involuntary psychiatric patients with drug problems there. http://www.ossipee.org/police-department/news/drug-and-alcohol-incidents

      A large percentage of NH’s prisoners are from the cities of Northern MA – Lawrence, Methuen, Lowell, Lynn, Haverhill – involved in moving drugs.


      • Another good one. My town has a little bit of this, as we have a route that runs off the highway and in between less good towns. Every time I see something on the police Twitter feed, it’s always something along that route.


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