The end of last week a study in the American Journal of Public Health claimed that there were more police feloniously killed in states that had more guns. The study got extensive news coverage on the TV networks such as NBC News, dozens of newspapers such as the Chicago Sun-Times, and international coverage such the UK Guardian. Yet, it took just a couple of minutes to read the paper and realize that the empirical work was done in a very non-standard way. There is a big benefit to using so-called panel data, where you can more accurately account for differences in crime rates across states or over time. This method is called “fixed effects.” Ask any academic who deals with this type of data, and they will tell you that these are basic controls that all papers in this area account for. Strangely the authors, David Swedler, Molly M. Simmons, Francesca Dominici, and David Hemenway, only control for the differences across states and not over time.
A couple of simple examples show why other studies on crime take into account these factors
Take the differences across places. Many people point out that the UK has both a lower gun ownership rate and a lower homicide rate than the US. Some use this to claim that gun control causes crime rates to fall. But the homicide rate actually went up by 50 percent in the eight years after the 1997 handgun ban went into effect. The homicide rate was still lower than that in the US, but there were lots of reasons it was lower to begin with, not the handgun ban.
The same point applies over time. Suppose a state passes a gun control law at the same time that crime rates are rising nationally. It would be a mistake to attribute the overall increase in national crime rates to the law that got passed. To account for that concern, researchers normally see whether the increase in crime rate for the state that had the change is greater or less than the overall national change.
Unfortunately, the American Journal of Public Health study doesn’t account for this last concern, and their results are extremely sensitive to this error. Here is a simple version of their regression explaining the number of police officers feloniously killed over the years from 1996 to 2013, but without accounting for the time effects that we just discussed. Before going through the results, the media coverage of this study is incorrect in claiming that more guns are associated with more police killings. What the journal article actually measures is not the gun ownership, but the percentage of suicides committed with guns (fsdsuicides). We have expressed our concerns about this measure many times, but since these authors and many other academic authors use this measure and the media is reporting this as gun ownership, we will use it here primarily for comparison purposes. This regression looks at the total number of police feloniously murdered with their measure of “gun ownership” and the number of police officers. In this regression, it appears that a one percentage point increase in the percent of suicides committed with guns increase, there is a significant 1.8 percent increase in the total number of police killed.
It seems hard to believe that Swedler, Simmons, Dominici, and Hemenway wouldn’t have tried accounting for these differences as their first estimates on explaining police deaths. The fact that they never mention how this alters their results is troubling. As usual, the AJPH was not interested in publishing a comment pointing out this sensitivity. For any media that might be reading this discussion, let us suggest that you contact an empirical economist or criminologist who deals with panel data of your choosing and ask them these simple questions. If you are dealing with panel data, how unusual is it for the authors of a peer-reviewed paper not to ever account for these changing differences over time? If they didn’t somehow account for this factor any place in their paper but doing so caused you to get the opposite results from what they claim, what would that do to your evaluation of their conclusions?
Just accounting for the changes in crime rates over time, completely reverses the claims made in the American Journal of Public Health. It now appears that a one percentage point increase in the percent of suicides committed with guns increase, there is a significant 2.25 percent decrease in the total number of police killed.
Including the other variables that they have used in their estimates along with the year fixed effects produce an even more statistically significant drop in police felonious killings. In that case, a one percentage point increase in the percent of suicides committed with guns increase, there is a significant 3.62 percent decrease in the total number of police killed.
The lowest reported rates of gun ownership were reported in the areas in which the admission of gun ownership is a felony. DC residents were going to tell the honky interviewers that they had guns in violation of the law. Sure.
Statistics can be manipulated into saying exactly what you want for the desired results. Most people don’t realize this. Thank you for pointing out to the liberals the error of their ways
When Communism lost its allure following WWII, many die-hard adherents went to ground in our universities. Today, their students are our children’s teachers and professors. They don’t teach how to think any more, but what to think. The socialist/communist agenda is more valuable to them than truth, as evidenced by the many “massaged” studies twisting reality to suit that agenda – and even innocent lives are less valuable to them than their agenda, as evidenced by “Gun-free zones:” target-rich environments, safe for killers, enabling high body counts that can be used to inflame the public against the only tools that can empower the weak to effectively deal with the rabid predators among us. These are the people calling for “comprehensive immigration reform,” without enforcing the laws we have, keeping us from learning exactly what needs reforming.
“When Communism lost its allure following WWII, many die-hard adherents went to ground in our universities.” Assuming that die-hard adherents were 20-30 during this time period, that would mean they’re 80-90 now and no longer teaching in our colleges. If they were older, they’re likely no longer with us.
Your theory fails when we apply arithmetic, I’m not going to bother looking for the logical errors.
“When Communism lost its allure following WWII, many die-hard adherents went to ground in our universities. Today, their students are our children’s teachers and professors.”…you need to utilize better reading comprehension before applying arithmetic to Conrad’s theory. Just trying to help.
I made this graph a few days ago. It’s in polish, but let me translate.
The left scale – homicides of law officers committed with guns in the United States per 10 milion poeple; the right scale – number of firearms in the United States per 1.000 people.
The data for these numbers has been gathered from two sources. 1965-1987, the data was taken from “Point Blank: Guns and Violence in America” by Gary Kleck (table 2.1). The methodology used by Kleck was applied to the figures obtained from the ATF for later years. The number shown is the cumulative addition of domestic manufacture plus imports minus exports. This does not count guns shipped to the U.S. military. The figures are rounded to the nearest million.
The numbers do not account for reduction of the gun stock due to wear and tear, loss, destruction or illegal exportation; or increases of the stock from illegal importation, individual or illegal manufacture, or acquisition from military sources.
Why is it so many worry about people who have legal firearms, and can protect themselves and others? Yet, they don’t seem to care much about those illegals (felons) who llegally use firearms to commit crimes, yes, mureder of children too.
It would seem, at least in the U S of A, that we would put our heads together, yes, to work on the problems of killings, suicides, robberies together? That would help solve the problem. As long as we fight each other, and make laws that will only allow criminals to own guns, we will solve the problem. Make it harder on the criminal who steals a firearm, owns one, etc. Make the laws match the crime. What is going to happen when bad people decide to stab, or decipatate others. Will there be a big push on bannind knives. Think about what we say. In the long run, someone very sinister is trying to keep firarms from the hands of legal, law adading citizens. Had it not been for people who don’t know what they are talking about, when it comes to making guns illegal, the publicity garnered would not have driven every Tom, Dick and Harry to go out and buy one. The majority of those legal weapons purchased by legal citizens, sit in homes, never used (They wee bought for home protection) yet those against guns seem to want everyone to believe that one out of two citizens is running around with a gun under their coat. Be real. God (ok, if you don’t believe, something/someone) gave you a brain use it. Know the facts, don’t play someone else’s music not knowing the name of the song. My very best wishes to all of you and may you think with your own mind, instead of doing what anyone tells you to do. My suggestion “think with your own mind, instead of doing what anyone tells you to do” is merely a suggestion. I am not trying to tell you that you have to. Most of us know how to relate racts to lies. Look at the picture, before you slash the rights of others, legal citizens, jus like you, and it will help you deal with the world better. Worry about ho our country is being illegally invaded. Worry how our government has gotten so corrupt that one has to serve but 4 years to collect a big retirement. Worry why those whom we compensate to keep us safe and alive, i.e., Military, Police, etc, are paid so little. Think for yourself. And, as long as criminals are bertter treated than Veterans who put their lives on the line for you, there will never be justice. I know, some of you will not agree with me, and that is fine. I still believe in you. That is what true law abiding citizens do, work and trust each other.
I agree that legally owning a gun does not cause people to shoot others, and that many of those who do shoot others own their guns illegally, But about your comment on decapitations and stabbings, I must say that we have yet to see gangs doing drive-by stabbings, and I’ve not heard of any mass decapitations either.
While I agree with the analysis that the study failed to control for major confounders, I’m pretty sure that the Constitutionally-recognized right to self-defense (with whatever is the current state of arms), does not hang in the balance for a “scientific” study. My rights are not subject to public opinion or cancellation by a simple majority.
I know they are just trying to lay some ground work so they can flaunt faulty statistics like the Kellerman study or some other tripe. I think that every study that has Bloomberg funding should be automatically distrusted and fluff journals with an obvious political agenda should also be excoriated. Letters to the editor and blog postings of their abuses should get them to rethink their nonsense.
Crime Prevention Research Council should know about about faked research. Been publishing it for years.
Melissa, if you can point to any errors in this post or in any other posts, it would be useful to hear them. Thanks.
Well Melissa, Prof. Lott has called you out. Please isolate the data you rely on for your claim that the research he published is fake. You have the data, don’t you?
Otherwise, what you said is libel and should be the subject of a civil prosecution. So, I’m going to sit back and wait for your data, because you would never libel or slander someone, right?
Did you notice that the researchers NEVER claimed that there were more police feloniously killed in states that had more guns?
They only looked at correlations between gun ownership and officer death rates, it can’t definitively say whether some other unseen factor may have been driving both.