The committee has confirmed this finding as is evident in its Tables 6-1, 6-2, 6-5 (first row), 6-6 (first row), and 6-7 (first two rows). This confirmation includes both the original data period (1977-1992) used by Lott and data that run through 2000. In view of the confirmation of the findings that shall-issue laws drive down the murder rate, it is hard for me to understand why these claims are called “fragile.”
The only exceptions to this confirmation are, to me, quite puzzling. Tables 6-5 and 6-6 suggest that RTC laws have no effect on murder rates when no control variables are entered into the equations. These control variables (which include all of the social, demographic, and public policies other than RTC laws that might affect crime rates) are essential to understanding crime. Suppose Professor Jones wrote a paper saying that increasing the number of police in a city reduced the crime rate and Professor Smith wrote a rival paper saying that cities with few police officers have low crime rates. Suppose that neither Jones nor Smith used any control variables, such as income, unemployment, population density, or the frequency with which offenders are sent to prison in reaching their conclusions. If such papers were published, they would be rejected out of hand by the committee for the obvious reason that they failed to supply a complete account of the factors that affect the crime rate. One cannot explain crime rates just by observing the number of police in a city any more than one can explain them just by noting the existence of RTC laws.
It is not enough to say that it is hard to know the right set of control variables without calling into question the use of economics in analyzing public policy questions. All control variables are based on past studies and reasonable theories; any given selection is best evaluated by testing various controls in one’s equations.
In addition, with only a few exceptions, the studies cited in Chapter 6, including those by Lott’s critics, do not show that the passage of RTC laws drives the crime rates up (as might be the case if one supposed that newly armed people went about looking for someone to shoot). The direct evidence that such shooting sprees occur is nonexistent. The indirect evidence, as found in papers by Black and Nagin and Ayres and Donohue [cited in Chapter 6], is controversial. Indeed, the Ayres and Donohue paper shows that there was a “statistically significant downward shift in the trend” of the murder rate (Chapter 6, page 135). This suggests to me that for people interested in RTC laws, the best evidence we have is that they impose no costs but may confer benefits. That conclusion might be very useful to authorities who contemplate the enactment of RTC laws.
Finally, the committee suggests that extending the Lott model to include data through 2000 may show no effect on RTC laws on murder rates if one analyzes the data on a year-by-year basis (Table 6-7, rows three and four). I wish I knew enough econometrics to feel confident about this