Saturday, April 11, 2015

MLB forecasters are more conservative this year

Every April, sabermetricians, bookies and sportswriters issue their won-lost predictions for each of the 30 teams in MLB. And, every year, some of them are overconfident, and essentially wind up trying to predict coin flips.

As I've written before, there's a mathematical "speed of light" limit to how much of a team's record can be predicted. That's the part that's determined by player talent. Any spread that's wider than the spread of talent must be just random luck, and, by definition, unpredictable.

Based on the historical record, we can estimate that the spread of team talent in MLB is somewhere around an SD of 9 games. Not all of that talent can be predicted beforehand, because some of it hasn't happened yet -- trades, injuries, players unexpectedly blossoming or declining, and so on. My estimate is that if you were the most omnicient baseball insider in the universe, maybe you could predict an SD of 8 games.

Last year, many pundits exceeded that "speed of light" limit anyway. I thought that there would be fewer this year, that the 2015 forecasts would project a narrower range of team outcomes. That's because last year's standings were particularly tight, and there's been talk about how we may be entering a new era of parity.

And that did happen, to some extent.

I'll show you the 2015s and the 2014s together for easy comparison. A blank space is a forecast I don't have for that year. (For 2015, I think Jonah Keri and the ESPN website predicted only the order of finish, and not the actual W-L record.) 

Like last year, I've included the "speed of light" limits, the naive "last year regressed to the mean" forecast, and the "every team will finish .500" forecast. Links are for 2015 ... for 2014, see last year's post.

 2015  2014
 9.32 11.50  Sports Illustrated
 9.07  8.76  Jeff Passan (Yahoo!)
 9.00  9.00  Speed of Light (theoretical est.)
 8.79        Bruce Bukiet
       8.53  Jonah Keri (Grantland)
       8.51  Sports Illustrated (runs/10)
 8.00  8.00  Speed of Light (practical est.)
       7.79  ESPN website
 7.92  7.78  Mike Oz (Yahoo!)
 6.99        Chris Cwik (Yahoo!)
 6.38  6.38  Naive previous year method (est.)
 6.34  9.23  Mark Townsend (Yahoo!)
 6.10  6.90  Tim Brown (Yahoo!)
 6.03  7.16  Vegas Betting Line (Bovada)
 5.46  5.55  Fangraphs 
 4.93  8.72  ESPN The Magazine 
 0.00  0.00  Predict 81-81 for all teams

Of those who predicted both seasons, only two out of eight increased the spread of their forecasts from last year. And those two, Jeff Passan and Mike Oz, increased only a little bit. 

On the other hand, some of the other forecasters see *dramatically* more equality in team talent. Yahoo's Mark Townsend dropped from 9.23 to a very reasonable 6.34. And ESPN dropped from one of the highest spreads, to the lowest -- by far -- at 4.93. 

Which is strange, because ESPN's words are so much more optimistic than their numbers. about the Washington Nationals, they write,

"It's the Nationals' time."
"They're here to stay."
"Anything less than an NL East crown will qualify as a big disappointment."

But their W-L prediction for the Nationals, whom they projected higher than any other team?  A modest 91-71, only ten games above .500.


In any case ... I wonder how much of the differences between 2014 and 2015 are due to (a) new methodologies, (b) the same methodologies reflecting a real change in team parity, and (c) just a gut reaction to the 2014 standings having been tighter than normal.

My guess is that it's mostly (b). I'd bet on Bovada's forecasts being the most accurate of the group. If that's true, then maybe teams really *are* tighter in talent than last year, by around 1 win of SD. Which is, roughly, in line with the rest of the forecasts.

I guess we'll know more next year. 

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