Projections, Predictions and Guns vs Cars

Welcome to “From the Archives”, where I dig up old posts and see what’s changed in the years since I originally wrote them.

Last week, while researching my post about definitions you should remember while discussing mass shootings, I came across a post from January of 2013 that warranted further investigation. It was my take on a Bloomberg News article that projected that by 2015 automotive deaths would surpass gun deaths. They had showed this chart:

My primary grouse was that they seemed to be extrapolating the 2015 data from the 2008 and 2009 data. I decided to take a look and see how the Bloomberg prediction had turned out.

Interestingly enough, at this point it appears to be a statistical tie. The Violence Policy Center has a chart up through 2014 showing a slight lead for motor vehicle deaths:

The Washington Post OTOH, gave them a tie (rates reported per 100,000 people):

According to this post, the numbers for gun deaths ended up being 33,599 and the car deaths were 33,736. It is interesting to note that Bloomberg underestimated the car deaths by a little less than 2,000 /year, and the gun deaths by about 600/year. So they were wrong in their assumption that motor-vehicle deaths would continue to drop at the same pace they had been, but right in their assumption gun deaths would continue to rise. I’ll give myself half credit on this one.  Of course, we do have one more year to go before we get the 2015 data, so I could still entirely eat crow.

It’s worth noting that the rise in firearm death through 2014 was entirely due to an increase in suicide rates. Homicide rates actually decreased during that time:

Someone remind me to check back in next year to see where we went with this!

5 Definitions You Need to Remember When Discussing Mass Shootings This Week

In the wake of the Orlando tragedy of last week, the national conversation rapidly turned to what we could do to prevent situations like this in the future. I’ve heard/seen a lot of commentary on this, and I get concerned at how often statistics get thrown out without a clear explanation of what the numbers actually do or don’t say.  I wanted to review a few of the common issues I’m seeing, and to clarify what some of the definitions are. While I obviously have my own biases, my goal is NOT to endorse one viewpoint or another here. My goal is to make sure everyone knows what everyone else is talking about when they throw numbers out there.

Got it? Let’s go!

  1. Base rate Okay, this is obviously one of my pet issues right now, but this is a great example of a time you have to keep the concept of a base rate in mind. In the wake of mass shootings, many people propose various ideas that will help us predict who future mass shooters might be. Vox does a great article here about why most of the attempts to do this would be totally futile. Basically, for every mass shooter in this country, there are millions and millions of non mass shooters. Even a detection algorithm that makes the right call 99.999% of the time would yield a couple hundred false positives (innocent people incorrectly identified) for every true positive.  Read my post on base rates here for the math, but trust me, this is an issue.
  2. Mass Shooting I’ve seen the claim a couple of places that we have about one mass shooting per day in this country, and I’ve also seen the claim that we had 4-6 last year.  This Mother Jones article does an excellent deep dive on the statistic, but basically it comes down to circumstances. Most people agree that “mass” refers to 3 or 4 people killed at one time, but the precipitating events can be quite different. There are basically three types of mass shootings: 1. Domestic/family violence 2. Shootings that occur during/around other criminal activity 3. Indiscriminate public shootings. If you count all 3 together, you get the “one per day” number. If you only count #3, you get 4-6 per year. While obviously all of these events are horrible, the methods  of addressing each are going to be different. At the very least, it’s good to know when we’re talking about one and when we’re talking about ALL of them.
  3. Gun Deaths Even more common than the confusion about the term “mass shooting” is the term “gun deaths”. This pops up frequently that I’ve been posting about it almost as long as I’ve been blogging and have made a couple of graphs (here and here) that have come in handy in some Twitter debates. The short version is that anything marked “gun deaths” almost always includes suicides and accidents. Suicide is the biggest contributor to this category, and any numbers or graphs generated from “gun death” data tend to look really different when these are taken out.
  4. Locations This is a somewhat minor issue compared to the others, but take care when someone mentions “school shootings” or “attacks on American soil”. As I covered here, sometimes people use very literal definitions of locations to include situations you wouldn’t normally think of.
  5. Gun violence Okay, this one should be obvious, but gun violence only refers to, um, gun violence. In the wake of a tragedy like Orlando, I’ve seen the words “gun violence” and “terrorism” tossed about as though they are interchangeable.  When you state it clearly, it’s obvious that’s not true, but in the heat of the moment it’s an easy point to conflate. In one of my guns and graphs posts, I discovered that states with higher rates of gun murders also tend to have higher rates of non-gun murders with r=.6 or so. In most states gun murders are higher than non-gun murders, but it’s important to remember other types of violence exist as well….especially if we’re talking about terrorism.

One definition I didn’t cover here is the word “terrorism”. I’ve been looking for a while, and I’m not I’ve found a great consensus on what constitutes terrorism and what doesn’t. Up until a few years ago for example, the FBI ranked “eco-terrorism” as a major threat (and occasionally the number one domestic threat) to the the US, despite the fact that most of these incidents caused property damage rather than killing people.

Regardless of political stance, I always think it’s important to understand the context of quoted numbers and what they do or don’t say. Stay safe out there.

Guns and Graphs Part 2

In the comment section on my last post about guns and graphs there was some interesting discussion about some of the data.  SJ had some good data to toss in, and DH made a suggestion that a graph of gun murders vs non-gun murders might be interesting.  I thought that sounded pretty interesting as well, so I gave it a whirl:

Gun graph 4

Apologies that not every state abbreviation is clear, but at least you get the outliers. Please note that the axes are different ranges (it was not possible to read if I made them the same) so Nevada is really just a 50/50 split, whereas Louisiana is actually pretty lopsided in favor of guns.  That being said, the correlation here is running at about .6, so it seems fair to say that states that have more gun homicides have more homicides in general. Now to be fair, this chart may underestimate non-gun murders, as those are likely a little harder to count than gun related murders. I don’t have hard data on it, but I’m somewhat inclined to believe that a shooting is easier to classify then a fall off a tall building.  Anyway, I pulled the source data from here.

While I was looking at that data, I thought it would be interesting to see if the percent of the population that owned guns was correlated with the number of gun murders:
Gun graph 5

Aaaaaaaaand…there’s no real correlation there. It’s interesting to note that Hawaii and Wyoming are dramatically different in ownership percentage, but not gun homicide rate. Louisiana and Vermont OTOH, have nearly identical ownership rates and completely different gun homicide rates.

Then, just for giggles I decided to go back to the original gun law ranking I was using, and see if gun ownership percentage followed that trend:

Gun graph 6

There does appear to be a trend there, but as the Assistant Village Idiot pointed out after the last post, it could simply be that places with lower gun ownership have an easier time passing these laws.


Watch the definitions

A quick one for a Friday:

I’ve blogged before about paying careful attention to the definition of words used in study results.  It is often the case that the definition used in the study/statistic may not actually match what you presume the definition is.

Eugene Volokh posted a good example of this today, when he linked to this op-ed in the Detroit Free Press.  It cites a spokesperson from the Violence Policy Center who states that “Michigan is one of 10 states in which gun deaths now outpace motor vehicle deaths”.

My knee jerk reaction was that seemed high, but my tired Friday brain probably would have kept skimming.  Then I read why Volokh was posting it:

The number of accidental gun deaths in Michigan in 2009 (the most recent year reported in WISQARS) was … 12, compared to 962 accidental motor-vehicle-related deaths. 99% of the gun deaths in Michigan that year consisted of suicides (575) and homicides (495).

To be honest, I had presumed homicides were included, but suicide death didn’t even occur to me.   I’d be interested to see how many of the vehicular deaths were suicides, my guess is the percentage would not be as high as in the gun case.  Either way, I’m sure I’m not the only one who didn’t realize what was being counted.

Watch the definitions, and have a fabulous Memorial Day weekend!