Many folks like to quote Bill Parcels' gem: You are what your record says you are. It is a simple phrase and one rings true. However, many question the truth of that statement. The following is a statistic known as the Pythagorean Expectation for Wins.
[the graphic below is not appearing nicely for everyone: the formula is as follows:
Win = (runs scored)^2 / ((runs scored^2)+(runs allowed)^2)]
The idea behind that formula is that runs scored and runs allowed are better indicators of talent than wins.
A few days ago, I put forward data that shows that extra inning winning percentage does not indicate whether a team is good or not.
Below is a simple graph comparing first half record, first half Pythagorean record, and first half 9 inning game record against second half record.
The data set is 2011 AL teams. Just 14 data points. What we see here is that all three methods are not particularly great approaches to predicting future success in 2011. However, the Pythagorean record does tend to reflect second half performance a little better than the other two.
It would probably be a good idea to repeat this for the past ten years and see whether these trends hold true. At this point, it appears there may be slightly better ways than wins to figure out who you are.