I blogged last year on a paper by Gordon DahlÂ and Stefano DellaVigna, looking at the impact of movie releases on violent crime. To jog your memory, here’s the abstract:
Does Movie Violence Increase Violent Crime?
Gordon Dahl & Stefano DellaVigna
Laboratory experiments in psychology find that media violence increases aggression in the short run. We analyze whether media violence affects violent crime in the field. We exploit variation in the violence of blockbuster movies from 1995 to 2004, and study the effect on same-day assaults. We find that violent crime decreases on days with larger theater audiences for violent movies. The effect is partly due to voluntary incapacitation: between 6PM and 12AM, a one million increase in the audience for violent movies reduces violent crime by 1.1 to 1.3 percent. After exposure to the movie, between 12AM and 6AM, violent crime is reduced by an even larger percent. This finding can be explained by the self-selection of violent individuals into violent movie attendance, leading to substitution away from more volatile activities. In particular, movie attendance appears to reduce alcohol consumption. We find suggestive evidence that strongly violent movies trigger an increase in violence; however, this increase is dominated by a substitution away from more dangerous activities. Overall, our estimates suggest that in the short-run violent movies deter almost 1,000 assaults on an average weekend. While our design does not allow us to estimate long-run effects, we find no evidence of medium-run effects up to three weeks after initial exposure.
Now I think this is a really interesting study, but all kinds of folks seem to be mis-interpreting it to mean that violent movies have no impact on crime. At the AEA session where it was discussed, there was some conversation about optimal subsidies for violent movies, and others have put a similar spin on it (the study even made it into the weekly Scientific American podcast).
As my emphasis above shows, the authors themselves are quite careful on this point: they know something about short-run effects, but not long-run effects. But if you need more convincing, imagine a study in which we had data on the number of Iraqi insurgents who watched “How to make an IED” movies. Such a study might well show that at times when more insurgents watched these movies, IED attacks were lower. Would you then suggest that the US government should be subsidising the production of “How to make an IED” movies, in order to keep the troops safe?