Prison Law Blog, a blog I enjoy very much, today posts the following graph to support the proposition that guns “cause” homicide, in the sense that the more guns are produced, the more homicides will follow.
The problem I see with that proposition, at least as supported by this graph, is that the sharp rises in gun production seem to follow, rather than lead, increases in homicide. This tends to suggest to me that increasing homicide rates drive demand for guns, which in turn drives production.
And how do we read the fact that in the period at the end of the chart — about 2004 onward — gun production has swung upward sharply, while homicide has steadily declined? Of course, it might be possible that increased gun production is leading the coming wave of homicides, and we will soon see the result of all those extra guns in circulation. But it’s also possible that other social forces have been driving gun purchases upward recently even in the face of a decline in homicide (and crime generally). (Increased political polarization during the Bush years and economic insecurity among the 99% would be my guess for likely candidates.)
(The same post also links to a this UN report, which apparently contains a neat chart showing the correlation between gun availability and homicide rates by country. I admit I haven’t looked at the report yet, but of course the same causality problem raises its head — how do we know countries with higher homicide rates don’t have incentives to liberalize gun laws? Or both variables might be tied to other cultural factors not shown. I’m not being flip — it’s just really, really hard to nail down the direction of causality arrows on these issues.)