I have read [no citation available :-( ] the actual crime rate is somewhat correlated with the number of young men -- say, aged 13-30 -- in the population. This would explain an increase in the 1960s followed by a decrease in the 1990s and beyond.
Actually, it's a little bit more complex than that, but you're basically right. Sociologists actually look at the crime rates for men vs women as an indicator of social equality. I believe that the crime rates for women are going up while they're going down for men. So it's difficult to correlate crime with sex.
That said, age does play a significant role in crime rates. Our population is aging, and that's probably the primary cause of the decreasing crime rate.
Possibly but why wasn't there a second spike with the Gen-Y baby-boom (born in the range of 1980-1999), a much larger group than the original Baby-Boomers?
The Gen-Y baby-boom is not a larger group than the original Baby-Boomers. However, there is definitely a noticeable Gen-y bump. I'm guessing that the most common ages for criminals are in the dip of that curve, maybe 20-24, which means the downward trend should soon begin to reverse if this correlation holds true.
edit: just realized that chart is from 2000; you're absolutely right that a second spike is missing.
Two significant changes that reduced the crime rate were the reduction of lead in the environment (lead exposure creates a number of changes in people which increase the odds of criminal behavior) and the widespread availability of abortion (unwanted children are more likely than the general public to become criminals).
The second is discussed in Freakinomics and the first was discussed in a follow-up article by the same authors. I've listed them in the order I did because my memory says that reductions in lead are believed to have had a greater impact on crime rates than increased abortions.
Because they are expending their mischievous energy on reddit and 4chan.
I'm joking, but the point is serious -- if youth are the main demographic to commit crimes, and our youth now spend a lot more time indoors/online... wouldn't it make sense that the internet is actually responsible for keeping hoodlums off the streets?
