America's serious crime rate is plunging, but why?

[...] Twenty years ago, the murder rate for the whole US was 9.8 per 100,000 people. It has fallen by nearly half, although it is still twice the rate in France.

It's not just murder. Robberies were down nearly 10% last year and 8% the year before.

There are a score of explanations offered by sociologists for collapsing crime figures, from theories that it is tied to legalisation of abortion or reduction of lead in fuel to the closing of mental institutions.

One theory has it that better and swifter medical treatment has reduced the number of murders by saving the lives of assault victims who would otherwise have died. But that doesn't explain why overall violent crime is also down.

Anti-gun activists note that the cities with two of the sharpest falls in murder rates, New York and Washington, have enacted strict gun control laws by US standards. Yet Houston in Texas, where some regard it as criminal not to own a gun, has also seen a sharp drop in homicides.

One of the most widely accepted explanations is also one of the most politically and socially sensitive – that the imposition of sharply stiffer prison sentences since the early 1980s, which has resulted in the US having the highest rate of incarceration in the developed world, has kept large numbers of criminals off the streets. Read more