More Junk Science for Gun Control

A study claiming to prove that Connecticut background check reduced the gun homicide rate by forty percent is junk science.

Well, if the FBI can do it for the cause of disarming the populace, others can produce junk science too. One recent study has claimed to “prove” that Connecticut’s background check established in 1995 lowered the murder rate from firearms by forty percent. The Reason.com blog mentions five problems with the study. I thought the first one really showed how arbitrary this “proof” is.

The researchers do seem to be trying hard. Obviously, they are facing a problem: we can see what happened in real Connecticut after these laws passed: the murder rate per 100,000 population started dropping significantly after 1996. Does that settle it? No, because very similar gun murder rate drops happened in most other states, states that did not have such tougher background laws instituted. The study’s own major chart shows all other control states largely moving in lockstep with Connecticut on murder rates.

So they can’t learn anything meaningful comparing what happened in Connecticut to what happened in most other states. So they create a “synthetic Connecticut” which they posit shows what would have happened in Connecticut minus the new laws. 

The “synthetic Connecticut” to which they compare the real Connecticut, and which fares far worse in gun homicides minus those supposedly life-saving laws, is derived from a “weighted combination of states that exhibits homicide trends most similar to Connecticut’s prior to the law’s implementation.” (It ends up being 72 percent Rhode Island, with a mix of Maryland and California tossed in.)

So basically, because the Rhode-Island dominated mix resembled Connecticut before the 1995 change in Connecticut’s law, we are supposed to assume that they were going to go in exactly the same direction for the next ten years without any real variance.

How do we know that synthetic-Connecticut really is a good marker for real Connecticut? The weight of that point seems to be almost entirely a pure case of believing that “past performance guarantees future results.” Without saying anything about why it was so or should be presumed to always be so, the authors note that in the past Rhode Island’s gun homicide levels matched Connecticut’s very closely.

[…]

The study says that “The third assumption [behind their results] is that there are no unmeasured confounders during the post-law period. This is an untestable assumption given the absence of randomization of PTP law implementation across states.” That seems to be an admission that there was no attempt to think of any reason that Rhode Island should be an outlier from national trends, except that of course it must still be matching what would have happened in Connecticut absent the background check laws, because it used to.

So, basically, Connecticut’s murder rate is the same as most other states and the background check doesn’t seem to make any difference. However, Rhode Island’s gun murder rate went up. So the researchers decided that Rhode Island demonstrates what would have happened in Connecticut without the background check.

Yeah, that totally proves it.