Evasive randomness

By his own admission, Dan Goodin has devoted a lot of time to unraveling the mystery of why the "random" playlists generated by music player software often seem anything but random:

The problem, it turns out, isn't that the programs aren't randomizing my playlists. They are. According to Jeff Lait, a mathematician and author of randomm3u, it's what's happening between my ears, specifically, in my expectations of what it means for something to be random.

To illustrate his point, Lait referred to a phenomenon statisticians call the birthday paradox. Roughly stated, it holds that if there are 23 randomly selected people in a room, there is a better than 50-50 chance that at least two of them will have the same birthday. The point: Mathematical randomness often contradicts our intuitive expectations of randomness.

What we want, Lait says, isn't a list that's been randomized, but one that's been stratified, or separated into categories that are weighted by a listener's preferences. A stratified playlist might select songs randomly but would be smart enough to throw out choices that, say, would repeat a band within 10 songs.