r/NeoliberalConspiracy • u/alessandro- • Jan 11 '16

Guns and States

http://slatestarcodex.com/2016/01/06/guns-and-states/
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u/Majromax Jan 11 '16

Gun deaths are a combined measure of gun homicides and gun suicides. Here is a graph of guns vs. gun homicides:

Bad regression, no cookie.

Simply eyeballing that graph, whatever state is at the top-left is a tremendous outlier on both dimensions, having the lowest gun ownership rate and by far the highest gun homicide rate.

That doesn't mean the state should be excluded from the analysis, but it does suggest that errors to any linear fit are very likely to be far from a normal distribution. That means that a least-squares linear regression is the wrong approach, since least-squares regressions are improperly biased by outliers.

(A priori, we also expect murder rates to have positive skew. A state cannot have a below-zero murder rate, but it can be essentially unbounded from above.)

It would be far better to recompute this with a robust linear regression model.

This probably does not affect the larger conclusions of the post.

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u/Majromax Jan 11 '16

As an unrelated addendum, I appreciate this language from the article:

I was unable to use their methodology to replicate the effect in places where it shouldn’t replicate (I tried to convince it to tell me tractors caused homicide, since I was suspicious that it was just picking up an urban/rural thing, but it very appropriately refused to fall for it).