Texas A&M University: Does Strengthening Self-Defense Law Deter Crime or Escalate Violence? Evidence from Expansions to Castle Doctrine

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5. Conclusion

In recent years, more than 20 states have strengthened their self-defense laws by
adopting castle doctrine laws. These statutes widen the scope for the justified use of lethal
force in self-defense by stating the circumstances under which self-defense is justified and
removing the duty to retreat from a list of protected places outside the home. In addition,
in many cases they also establish a presumption of reasonable fear and remove civil
liability. Thus, these laws could hypothetically deter crime or, alternatively, increase
homicide.

 Results presented indicate that expansions to castle doctrine do not deter crime.
Furthermore, our estimates are sufficiently precise as to rule out moderate-sized deterrence
effects. Thus, while our view is that it is a priori reasonable to expect that strengthening
self-defense law would deter crime, we find this is not the case.

More significantly, results indicate that castle doctrine laws increase total
homicides by around 8 percent. Put differently, the laws induce an additional 600
homicides per year across the 21 states in our sample that expanded castle doctrine over
this time period. This finding is robust to a wide set of difference-in-differences
specifications, including region-by-year fixed effects, state-specific linear time trends, and
controls for time-varying factors such as economic conditions, state welfare spending, and
policing and incarceration rates. These findings provide evidence that lowering the
expected cost of lethal force causes there to be more of it.