source: Cheap Talk
As Cheap Talk explains:
How often should we expect a basketball game to end tied after 48 minutes of play? At first glance it would seem pretty rare. If you look at the distribution of points scored by the home teams and by the visiting teams separately, they look pretty close to a normal distribution with a large variance. If we made the crude hypothesis that the two distributions were statistically independent, then ties would indeed be very rare: 2.29% of all games would reach overtime. . .(via Coyote Blog)
But overtime is almost 3 times more frequent than this: 6.26% of all NBA games are tied at the end of regulation play. And games decided by just a few points are surprisingly rare: It is more likely to have a tie than for the game to be decided by two points, and a tie is more than twice as likely as a one-point difference.