The team that scores the most runs in one game wins. So based on the number of runs we score in any particular game we win, our win percentage for that game is expected to be 100%.

is a valuable statistical tool. It’s best value is as an analytical method of converting runs allowed/scored into wins/losses if you are modeling the effect of personnel changes for a team. As a predictive tool, it is much more crude, IMO. Sure, I agree with Dying Quail, above, that looking att differences between a team’s pythag prediction and the actual record should make you think, and one should be aware of it. But also keep in mind that the Pythag is based on certain assumptions regarding run distribution and that those assumptions are capable of being changed by managerial tactics, unusual personnel combinations, or unusual consistency patterns.. One of the most likely ways that team should be expected to do better than its Pythagorean record is if it has excellent late inning relief work, and I think that we can agree that Valverde has been dominant during this second half run by the Astros. This article in HT suggests that there are reasons why the D-Backs should have been expected to outperform their Pythag:
Interestingly, Valverde is a big part of the explanation posed for the D-Back’s overperformance. Also the manager’s strategy of “giving up” on blow outs, keeping terrible pitchers in the game to give up more and more runs is discussed. I think Cooper seems to follow this tactic too. The article points out that the D-Backs were 15-22 in blow-outs, which is unexpected for a 100+ win team. That seems consistent with AstroAndy’s tabulation of a 6-14 record for the Astros in blow outs.
Another characteristic which has been shown to be related to Pythag overperformance occurs when a team’s pitching is much more inconsistent than its offense. I think we can agree that the Astros’ pitching has been inconsistent this season…whether the offense has been more consistent, well I’m not sure, but I suspect so.
If you are interested in the topic of “explaining” Pythagorean discrepancies, try this article:
http://mvn.com/mlb-stats/2007/09/06/what-do-pythagorean-residuals-really-measure/
One run game winning percentage is highly predictive of Pythag overpoerformance, and the article points out the obvious point that every run scored above the winning run is a wasted run, and that teams which waste fewer runs will overperform.

I’m not really arguing one way or other, with respect to the Astros’ situation, because I don’t know for certain how much, if any, the Astros should be expected to out perform Pythagorean W/L numbers. But it’s an interesting topic. And I do see some characteristics associated with the Astros which seem to be among those which accompany overperformance.

Inspired by Astro Andy’s diary and his talk of high leverage situations, I sat down and (armed with trusty Excel sheet) I took a look at the majors, its win percentages, its expected win percentages, and its winning percentages in one-run games (high leverage games, natch).

The Astros, in outperforming their Expected win percentage by 50 points, are second in the majors in that metric, behind only the Angels, who are at .066.

But more interestingly, the ’Stros are the only team in the majors to have outperformed their expected record, while still having a losing record in one-run games. Houston is 19 – 20 in one-run games, for a .487 percentage, which is 18th best in the majors.

That’s a statistical disconnect that no other team in the majors can show. In all other cases, a team’s having outperformed their expected record predicts a winning record in one-run games, and a team having underperformed its pythagorean record indicates a losing record in one-run games. (The Cards, the Mets and The Gnats all have records equivalent to their pythagorean records, and all have losing records in one-run games).

I made a graph putting the expected – pythagoran number along the horizontal and the 1-run percentage along the vertical, and the astros are the only ones in the second quadrant. Everyone else is in the lower left or the upper right.

So what’s my point?

Ha. I don’t know. Maybe I’m just reinforcing the idea that the ‘Stros recent (and otherwise) hot streaks are sheer anomaly. After all, we all know the Astros just aren’t that good.

But I’m seeing that for many of the other teams who have done better than their expected record, like the Angels, you can point very quickly and very easily at their unrealistic record in one-run games as the reason.

With the Stros, you can’t. I read this book where Bill James seemed to sugges that managers should be credited for their teams consistenly finishing better than their expected records. But that would mean giving credit to Coop . . . and I’m not sure I’m ready to do that, either.