Of the division-leading teams six weeks into the 2005 season, the Angels and Cardinals are pretty much doing what was expected of them. The four other teams in first place the Orioles, White Sox, Braves and Dodgers have surprised almost everyone by their hot starts. The Sox own the best record in baseball by a substantial margin, while the O's are tied with the Cards for the second-best record.
Who'da thunk it? Of course, it's still early in the season and plenty of unexpected things can happen. But it wouldn't be the nation's pastime if the fans and pundits weren't busy trying to figure out if these surprising teams are for real.
A good way to try to answer that question is to look at the history of early season records for all teams. Each team has a true unknown win probability that is represented by a sample from the actual record for the season. We can make a pretty good guess at the true value, however, since we know exactly the variation in all teams (measured by the standard deviation in wins for a season) and we also know what the expected variation would be if all teams were truly equal.