Summary: rain reduces the probability of interaction with people. Interaction with people correlates with homicides. So rain inversely correlates with homicides.
I have a buddy who lived in NYC for a decade. I was there for a visit a few years ago and asked him if he ever had any trouble, getting mugged or hassled, because he walked everywhere at every time of day.
He replied with, "Meh. Criminals are lazy. They don't want the effort of earning something they can simply take, so they don't have jobs. I'm six feet and I walk fast. I'm like the strong wildebeests at the front of the herd. The criminals will wait for a weak one to fall behind. Easier."
By his logic, lazy murderers probably prefer to get their murder on without getting wet.
I walk a lot, too. An interesting anecdote, which dovetails with your "wildebeest" analogy.
I'm 6'2". I have gray hair and beard, but normally am clean shaven (head and face). I walk through a somewhat tough area, and no one ever bothers me. Yes, I walk fast and with purpose.
I was having razor issues and ended up growing a (white) beard for a while. I was completely floored by the amount of crap I got from random people. It was aggressive stares, and in some cases aggressive behavior. On a single day I came close to an altercation with two people.
It was pretty obvious to me that I looked much older, so I shaved the beard and head. The next day, people were back to ignoring me.
Have you considered a straight razor (the old kind they used to have in barber shops)? A good one is a little expensive (a couple hundred bucks for a brand like DOVO) but will last you for decades if you take care of it. I've heard they're good for people who get razor burn or ingrown hairs from normal safety razors (since they are way sharper).
Actually, I was being generic with the "razor" term. I actually use an electric shaver. I never had much luck with razors, though I never tried a straight razor. (The issue I had was that once it grows past a certain length, I have to let it grow out for a week and whack it with a beard trimmer before I can use the electric razor. Otherwise, it hurts.)
I had that theory for a while. I figure if you're trying to avoid being mugged, you don't have to be invulnerable, just the second most vulnerable person a mugger can see. If we had better data, we could even figure out if, e.g., a guy listening to an iPod is more vulnerable than a woman who isn't, or if it depends on age, or what.
Question: If that is (one of) the reason(s) behind, then the correlation should be observed universally across the country, or even across the world, is that the case?
I think the article mentioned that there was insufficient data.
Without an ability to test it, I'd hypothesize that rain matters more in areas where people are more likely to be outside. In areas that are more car-dominated it may matter less because you can cause trouble while staying dry.
I think people are so excited about the upcoming rainbows that they forget about all bad things. Searching Twitter for rainbow just brought up a ton of results from people in New York going "Awwww" and "dancing under the rainbow"... quod erat demonstrandum?
Maybe with the open data push they could plot suicide rates against national holidays. Snopes says it is false, but I have always personally felt that there is a corrolation. http://www.snopes.com/holidays/christmas/suicide.asp
The rain wave going on in the Northeast raises the question - is the reduction in crime on rainy days a temporary phenomenon, or is it something more fundamental? In other words, would an extremely rainy decade see a reduction in crime due to the rain? I'm guessing it would be a reduction, but not as great as the daily ones seen. After all, people adapt, with umbrellas and such.
A similar phenomenon to look at is the increased birth rate observed nine months after blackouts. Blackouts probably cause some births that would have occurred in close proximity to the nine-months-later period to move to that time period, as well as causing others to occur that would not have otherwise (accidents).
