Líneas de Negocio y Productos

Health and Welfare (AIHW 2009), there are some concerns that a change in the Australian Bureau of Statistics’ method of collection of data on external causes of death after 2002 might have led to systemic underestimates of suicide deaths in particular. If this underestimation were consistent throughout Australia, then underestimates would not affect our results, since we include a full set of year fixed effects. However, if there were differences in under-reporting rates by state, and these happened to be correlated with the firearm buyback rate, our estimates might be biased. There is evidence that there were differences under-reporting by state. Interestingly, however, the AIHW report shows that Tasmania and the Northern Territory, which had the highest buyback rates, had almost no under-reporting, as did the Australian Capital Territory which had the lowest buyback rate (see Table 7). This would certainly not give much reason, then, to think that the results in this paper

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Table 11.Instrumental variable estimates of the effect of the gun buyback rate on death rates (1968 to 2006). Guns coefficients represent the impact of buying back 1,000firearms

Basic models Including Port Arthur Dummy

Firearm Non-firearm Total Firearm Non-firearm Total

No trend Trend No trend Trend No trend Trend No trend Trend No trend Trend No trend Trend Suicide (Instrument = estimated gun ownership, 1989 and 1992)

Guns bought −0.312*** _{−0.675*** 0.172 0.024 −0.139 −0.652 −0.327}*** _{−0.803*** 0.171 0.006 −0.157 −0.797} t-statistic (5.20) (7.48) (0.41) (0.07) (0.37) (1.77) (5.49) (7.14) (0.40) (0.01) (0.40) (1.82) Hausman test Difference 0.015 −0.106 −0.624 −0.504 −0.608 −0.611 0.011 −0.153 −0.628 −0.540 −0.617 −0.693 t-statistic (0.24) (1.19) (0.94) (0.92) (0.98) (1.03) (0.19) (1.23) (0.94) (0.95) (0.99) (1.07) R2 0.7309 0.7469 0.4752 0.6854 0.3822 0.5805 0.7344 0.7437 0.4751 0.6850 0.3825 0.5802 Number of obs. 312 312 312 312 312 312 312 312 312 312 312 312

Homicide (Instruments = gun ownership and % of suicides that arefirearm)

(continued) American Law and Economics Review V12 N2 2010 (509 – 557)

Basic models Including Port Arthur Dummy Guns bought −0.122 −0.255*** −0.216 −0.156 −0.337 −0.411 −0.077 −0.042 −0.217 −0.171 −0.293 −0.213 t-statistic (1.36) (3.49) (0.58) (0.46) (0.73) (1.05) (0.76) (0.34) (0.57) (0.47) (0.61) (0.44) Hausman test Difference −0.022 −0.055 0.117 0.078 0.255 0.312 −0.015 −0.024 −0.067 −0.061 −0.081 −0.086 t-statistic (0.34) (1.13) (0.42) (0.30) (0.74) (1.10) (0.20) (0.27) (0.24) (0.22) (0.23) (0.24) R2 0.4024 0.4371 0.8157 0.8415 0.8327 0.8647 0.6195 0.6429 0.8157 0.8415 0.8428 0.8347 Number of obs. 312 312 312 312 312 312 312 312 312 312 312 312

Dependent variable is the identified death rate, in deaths per million people. Gun buyback rate is measured as guns per thousand people. Estimates from a panel model, with annual observations at the state level. All specifications include state and yearfixed effects, but not socio-economic controls. The panel to the right includes the Port Arthur dummy. Instruments used are (a) the estimated rate offirearm ownership from the 1989 and 1992 ICVS surveys (figures provided inTable 2) and (b) the average percentage of suicides undertaken with a

firearm between 1994 and 1996. (We assume that thefirearm ownership rate in the ACT is the same as that in NSW.)Table 3shows thefirst-stage regressions in the stripped down version of the model. Results are similar for the panel model. Robustt-statistics in parentheses, clustered at the state level.

* significant at 10%.

** significant at 5%.

*** significant at 1% level.

Do Gun Buybacks Save Lives? Evidence from Panel Data 549

would be biased downwards. Further, there appears to be little reason to think there is much mis-reporting in the data on firearm deaths. The AIHW report records very few cases in their audit of the data where firearm deaths were mis-coded.

Unlike other studies, our results are relatively insensitive to the particular time period chosen, and the results inTable 5, which show the dynamic effects of the NFA, show that the key estimates of reductions in firearm homicides and suicides are not an artifact of the years after 2002. Indeed, if anything, the only results that do appear to be affected by the post- 2002 years are those on non-firearm suicides, which show a larger increase in non-firearm suicide rates in states that had higher buyback rates. As discussed earlier, this is the most important reason for the overall positive point estimates of the effect of the NFA on non-firearm suicide rates. If this is a result of the change in data collection practices in 2002, then our results are if anything stronger.

Nonetheless, concerns about the effect of these data problems on our results may remain. Unfortunately, there is no plan to revise ABS estimates for death rates between 2002 and 2006, so we cannot expect significant improvements in these data in the future. We can, however, examine whether there is any evidence that a recoding of suicides to other external causes of death—in particular accidental deaths or deaths of undetermined intent—could have affected our results. We do this by simply running the same set of regressions for cases of accidental death and deaths of undetermined intent that we ran for homicides and suicides. If wefind that the NFA appears to have led to an increase in either of these categories of death, we would be concerned that our results of a relatively large fall infirearm homicide and suicides in states with higher buyback rates represents a recategorization of deaths, rather than a decrease in actual deaths. In the case of firearm deaths, the small numbers of accidental deaths and deaths of undetermined intent mean that we are forced to group these together. They can be separated in the case of non- firearm deaths, however. The estimates using Equation (1) show a very small negative and statistically insignificant (p-value 0.344) effect of the buyback rate on deaths due to firearm accidents and deaths of undetermined intent. There is no reason to think, then, that the estimates on firearm homicides and suicides in particular are a result of mis- classification of deaths. The results are the same for non-firearm deaths

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in those two categories, for all accidents, all deaths of undetermined intent, and for deaths due to ill-defined causes (p-values 0.306, 0.247, 0.922, and 0.594, respectively).27