Did the gun buyback reduce gun homicides or suicides? According to a new paper in the British Journal of Criminology by Jeanine Baker and Samara McPhedran, it didn’t. (The two have been criticised for their affiliations to the gun lobby, but I don’t think that invalidates their study.)
The paper’s methodology starts from an important insight: since gun homicide and suicide rates have been trending downwards over recent decades, we should compare the efficacy of the gun laws not against the pre-1996 rates, but against the extrapolated trends.
Like the best papers, this approach can be shown with a simple graph. The dashed lines in the chart above (figure 4A in the paper) depict 95% confidence intervals for the trend in gun homicides from 1979-96, extrapolated forwards. The solid line is the actual gun homicide rate.
If the buyback cut gun homicides, we should have expected the solid line to break through the bottom dashed line. This would tell us that fewer gun homicides happened than the extrapolated trend. This didn’t happen, so Baker and McPhedran conclude that the buyback didn’t work. As Jeanine Baker said on the AM program yesterday:
In 1996 we were told that taking the… buying back those civilian firearms, off those licensed firearms owners would make society safer and it would reduce firearm deaths. The evidence isn’t there to support that.
But let’s just look at that graph again, and see what would have had to happen for the gun buyback to work. In 2004, the bottom dashed line hits zero. For the solid line to go below the dashed line, the gun homicide rate in Australia would have to be negative in 2004, and extremely low in earlier years. (Ironically, one of the reasons that their statistical test has so little power is that the mass shootings of the 1980s and 1990s made the gun homicide rate extremely volatile, and the 95% confidence band very wide.)
In other words, Baker and McPhedran have set the gun buyback an impossible test. Just because gun buybacks don’t lead to negative gun homicide rates, it doesn’t follow that they don’t work.