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Wednesday, July 8, 2015

Another Anti-Gun "More Guns Equal More Crime" Study

Tuesday, Live Science touted a new study by Harvard Injury Control Research Center Director David Hemenway and fellow researchers Michael Monuteaux, Lois K. Lee, Rebekah Mannix, and Eric W. Fleegler that makes the claim that guns don't deter crime:
"We found no support for the hypothesis that owning more guns leads to a drop or a reduction in violent crime," said study researcher Michael Monuteaux, an epidemiologist and professor of pediatrics at Harvard Medical School. "Instead, we found the opposite."
The Crime Prevention Research Center got a copy and found that the study did not test the theory that it claims to have studied.  CPRC notes that the study doesn't test whether increased gun ownership causes crime rates to increase, and is "far too simplistic and doesn’t include even the basic control variables that are typically included in other crime studies."
Here is a simple example.  Many people point to the fact that the UK has both a lower homicide and gun ownership rate than the United States.  The claim is often made then that the reason that they have a lower homicide rate is because they have fewer guns.  However, this ignores the fact that the UK homicide rate actually went up after their 1997 handgun ban or after their other very strict earlier gun control regulations.  The UK homicide rate still remained low relative to the US, but it was higher than it otherwise would have been.

The point here is simple: there are lots of reasons why the UK homicide rate was lower than that in the US before they even had gun control.  The question that needs to be asked is how the UK homicide rate changed relative to that in the US after its gun control regulations went into effect.  To do this, you have to control for the fact that the UK had a much lower homicide rate to begin with.  Statistically you do that by having what are called geographic “fixed effects” (dummy variables that pick up the average difference in each jurisdiction that you are examining).  Any test would also do the same thing by year so as to account for any national trends in crime rates.  So, for example, crime might have been falling nationally, but was it falling relatively more in those states that were getting more gun ownership.
And that's not all.  Anti-rights researchers tend to cherry pick the data they use to prove their hypothesis and this study is no different:
The controls that are being used in this paper can’t begin to account for the differences in crime rates.  The regression estimates reported in Table 2 don’t tell what percent of the variation in crime rates are being explained by the variables used in these regressions, but I am willing to bet that it is less than 10 percent.

Yet, this paper in the American Journal of Preventive Medicine doesn’t account for either of these factors.  It is essentially making a purely cross-sectional comparison across states.  On account of that, if they had included Washington, DC in their estimates (with its high crime rates and low gun ownership), it would have dramatically altered their results.
This is another study that appears to be swimming up stream as public opinion is firmly on the side of gun ownership.  Even cherry picking data probably won't change that fact.

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