If you have hayfever, you'll know that when the pollen count is high you get congested, your eyes are itchy, and you feel lethargic and miserable. In fact, you don't feel like doing anything at all. This, it turns out, also applies to pollen-suffering criminals.
A study published in the Journal of Health Economics has found that when the pollen count is unusually high in large cities, violent crime goes down by a significant amount.
"Leveraging daily variation in local pollen counts in 16 US cities, we present novel evidence that violent crime declines by approximately 4 percent on days in which the local pollen count is unusually high," the authors write in the study.
"While this might sound like a small behavioral response, it is on par with the change in crime that would be expected to accrue from a 10 percent increase in the size of a city’s police force."
The team looked at crime levels in cities including Chicago, Georgia, and New York. They found that whilst there was a noticeable decline in violent crimes when pollen was high, this effect wasn't seen on property crime, which generally requires more pre-planning. Pre-planned crimes, it appears, are not canceled by criminals after they check the pollen count.
The team suggests that the reason the decline in violent crime is happening is not some strange effect of pollen on the brain chemistry of allergy sufferers, nor was it that people had less opportunity to commit crimes because they were remaining indoors away from the pollen. There was a decrease in domestic violence too.
"Instead, the primary way in which these allergies affect people may be through the manifestation of the physical symptoms of illness which we argue changes the costs and benefits of offending as well as of victim precaution," they write.
"Given that the effects we observe are driven by a decline in residential, mostly family violence, despite the fact that, if anything, there is more residential interaction on high pollen days, this not merely a story about a change in opportunity or routine activities."
"Violence responds to other situational factors which shift the costs and benefits of offending and precaution: malaise driven by pollen allergies."
In short, people may be too drowsy from hayfever to commit crimes. The authors say that this shows how sensitive crime is to health shocks, and it's not just that the crimes are being delayed either. The study found that on high pollen days violent crime was reduced whilst individuals who may have committed violence were incapacitated due to allergies, but there was no corresponding increase in crime in the following days as they recovered.
"Our results do not show evidence of temporal displacement or state dependence, and hence the data are most consistent with the proportion that high pollen days prevent crime rather than delay it."
So, I guess, if you want to prevent crime invest in pollen canons rather than police?