[bsimpson]

It depends. They also rely on the element of surprise. Everyone I know who's been mugged or seen one happen on public transit has had something grabbed right as the doors are closing, so the thief slips away before you have time to squeeze through the crowd to run after.

[tomkarlo]

When someone does that, everyone on the subway car sees it. When someone gets pick-pocketed, nobody sees it. So there's a major sampling bias.

That said, I've also seen some NYT articles saying the true "pick pocket artists" are a dying breed, because younger criminals don't want to spend the time learning it and the potential take from a wallet has gone down as folks carry less cash.