In previous years, the various versions of Baseball Prospectus' Playoff Odds Reports were slow to respond to changes in lineups. All of them required the team to start playing differently -- sometimes as a result of trades or injuries -- before any change would be seen in the playoff odds of the various contenders, and those changes would be pretty seriously depressed by the weight of all the games that had come before.
This year, the PECOTA-based version of our playoff odds is being entirely set by our projections of player performance. A trade or injury has an immediate impact on the team's expected performance; we can anticipate the change in team performance without waiting for the signal to appear, and its effect on the postseason odds is immediate.
It turns out that the team that did the best job of improving their chances at a playoff spot with July moves was the Cardinals, who essentially replaced a Chris Duncan/Rick Ankiel combo projected to hit for about a .260 Equivalent Average (EqA) with Matt Holliday, projected to hit about .315. That's worth 15 runs on the rest of the season. They also picked up Julio Lugo, a significant upgrade at the plate from Brendan Ryan for at least part-time play; having Lugo and Ankiel as your main spares allows some addition by subtraction, with the ripple effect of their jettisoning some of the fringe players on the roster. The Cardinals' expected winning percentage improved 18 points as a result of all the moves, and their playoff chances increased from 59 to 69 percent.
The rest of BP's post-deadline playoff-odds analysis is for ESPN Insiders.