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State of the Rays: The predictive value of Run Differential

Brian Blanco

Is there still hope for the Tampa Bay Rays?

No team has yet to dip below five games back in the division, but a few losses in Anaheim are dimming the normally bright outlook of the Rays, at least according to ESPN's leaderboard:

Toronto 23 22 0.511 1.0 38.9
New York 23 20 0.535 - 33.2
Baltimore 22 20 0.524 0.5 31.7
Boston 20 23 0.465 3.0 27.3
Tampa Bay 19 26 0.422 5.0 11.1

Notice the filter is not set to games back or to winning percentages. It's not necessarily set to wins either. I had filtered this list on run differential:

Toronto 215 208 +7 Lost 1 5-5
New York 188 196 -8 Lost 1 5-5
Baltimore 167 175 -8 Lost 2 4-6
Boston 175 187 -12 Lost 4 4-6
Tampa Bay 179 201 -22 Lost 2 4-6

Things are starting to get real when it comes to run prevention. The entire division is one of strong-performers and general suck at the same time, keeping all teams competitive, but the run differential is beginning to be most telling.

Earlier this month Russell A. Carlton ran the history of season results against run differentials and found a 0.7 correlation beginning at game 40 on the season. In other words, forty games is the point where the picture becomes more clear than not, that true talent is more real than aberration. 40 games appears to be when the end of season standings first start to take shape.

There are two problems with declaring the season over, though. First of all, a 0.70 correlation is still only a coin flip in terms of probability, which is what this season's mantra has been for the AL East. Second, run differential is a reflection of the past. At forty games we now see a better-than-50% probability the run differentials have the same standing within the division at year end, but that applying data from a restricted set (1962-2013).

Carlton later applied Cronbach's alpha to the same data set (a process of running every combination of data against itself, instead of relying on reality's limited sample set) and found stability at 140 games. According to Cronbach's alpha, the best signal won't break through the noise until half that number, when you are more than half way to stability. In that scenario, the future is better conveyed at 70 games.

By that mark, we have 25 games until run differential becomes predictive, but having surpassed forty games I'm willing to say this team is likely the worst of the division. I'm also willing to place that blame solely on the shoulders of the starting rotation, where the Rays have been using three replacement pitchers.

Alex Cobb is scheduled to return this week, suddenly ahead of schedule and ready to contribute after performing at ace-like levels until a strained oblique last month. His addition should slot Cesar Ramos back to the 'pen -- he of 5.04 ERA, 5.18 FIP, -0.1 WAR -- and add some like to the rotation, but the Rays will need some stronger performances from the rotation mainstays.

David Price has been pitching to contact more often that he should, Chris Archer has been pitching away more often than he should, and Odorizzi has only just found success after the first time through the line up. Stronger performances from each, along side Erik Bedard's pleasant 2.97 ERA and 3.01 FIP, should finally add some support to what has been a fairly strong performance from the position players.

The Yankees and Blue Jays are heating up, this is no time to sit idly by. The Rays staved off disaster in Seattle, then succumbed in Anaheim, but will have opportunities against Oakland -- who leads baseball in run differential by a long shot -- Boston, Toronto, then Boston again to prove where they belong in the standings.

It's not over, but it ain't pretty. The pressure will be on the Rays to keep pace this week, and then triumph on the road if they want to sneak back into contention.


What are the others saying?

Baseball Prospectus's playoff odds still expect the Rays to lead the division at season's end with a .520 win percentage, and still assigns an >20% playoff mark, but still has Tampa Bay fourth in the standings. There are seven teams in the AL with worse odds on the page, putting the Rays right in the middle of the pack.

Fangraphs, on the other hand, is far more bleak, giving the Rays a 16.3% change at making the playoffs, fifth from the bottom. At least Vegas remains optimistic.