Weak Tests and Strong Conclusions: A Re-Analysis of Gun Deaths and the Australian Firearms Buyback
Using time series analysis on data from 1979-2004, Baker and McPhedran (2006) argue that the stricter gun laws introduced in the National Firearms Agreement (NFA) post- 1996 did not affect firearm homicide rates, and may not have had an impact on the rate of gun suicide or accidental death by shooting. We revisit their analysis, and find that their results are not robust to: (a) using a longer time series; or (b) using the log of the rate rather than the level (to take account of the fact that the rate cannot fall below zero). We also show that claims that the authors had allowed both for method substitution and for underlying trends in suicide or homicide rates are misleading. The high variability in the data and the fragility of the results with respect to different specifications suggest that time series analysis cannot conclusively answer the question of whether the NFA led to lower gun deaths. Drawing strong conclusions from simple time series analysis is not warranted, but to the extent that this evidence points anywhere, it is towards the firearms buyback reducing gun deaths.
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