“We kind of like our team. If you look at the run differential, we should be a .500 team. We’re not. At the same time, it doesn’t mean we should throw everyone overboard.” – Sandy Alderson
These words, uttered by Mets GM Sandy Alderson last week (in an interview with Jon Heyman for CBSSports.com) set off a firestorm in the Mets universe of newspaper columns, blogs, and on twitter. Much of the commentary was critical of Alderson, and to be fair, Alderson’s Mets deserve plenty of criticism. Was he deflecting blame? Is his head buried too deep in the spreadsheet to see that the Mets are actually “what their record says they are”?
The short answer is: No, Alderson is actually right.
Alderson’s use of “run differential” is spot-on, and deserves examination by (and explanation to) this passionate fan base. Say what you will about this team, but the concept of “run differential” (and its sister, “win expectancy”) are not just hocus pocus or advanced statistical mumbo jumbo. In fact, run differential is the simplest thing you can imagine.
Baseball is a game, and games have elements of chance in them. When chance plays a role, sometimes inexplicable things can happen. Scatter nine singles in a game and you might get shut out. String together nine singles in a row, and you might score seven runs.
Similarly, imagine flipping a coin and rooting for tails. Perhaps the first ten times you flip the coin, heads comes up seven out of ten times. If you were wise, you would look at that distribution and say “I still expect tails to come up around 50 percent of the time in the future.”
That is kind of what run differential does. It doesn’t undo the past, but it can help you predict the future. Run differential keeps a tally of all the runs scored and runs against each team in a given season. From those, you can extrapolate a number of expected wins. Generally, a team that scores more than it allows will win more than it loses, while a team that scores the same number of runs as it allows will, generally, in the long run, end up around .500. It’s a simple concept.
But how well does it work? Luckily, smarter men than I have tackled that question. Russell Carleton of Baseball Prospectus wrote a fantastic column about the correlation between run differential and actual wins earlier this year. He explains:
In general, I like to look for the point where the correlation reaches .70. For the uninitiated, 0 means that there’s no relationship between the two numbers, and 1 means there’s a perfect relationship between them. It’s a matter of how close you want that number to be to 1 before you feel comfortable, and you can see a chart below of how the correlation approaches 1.0 as the season goes on. The correlation hits .70 after 39 games. So, around the 40-game mark—mid-May—run differential starts to be a good predictor of what things will look like at the end of the year.
The more games you have played, the more accurate run differential becomes at predicting how good your team is. Which makes sense — the more games you play, the less noise there is in the number thanks to things like blowouts, and strength of schedule and streaks.
The Mets have now played over 90 games — so the correlation at this point between run differential and wins is somewhere around .86, which is quite high (note of course that the line in the chart above never reaches 1.0 — and the reason for that is because no matter how many games you play, run differential will never exactly equal the team’s record in all cases.) Once you’ve played 90 games (almost a thousand innings!) we know who you are.
Regardless of how your gut feels about it, run differential is a damn good way of predicting final records. If you’d like some more concrete proof about the correlation between the two, check out this excellent bit of research from the Star-Ledger:
The recent history supports this claim. In the past six full seasons, beginning with 2008, 95 teams have finished the year with a positive run differential and 86 of them have also had a winning record. And three of the teams that didn’t finished at .500. So if the Mets were to finish below .500 this season they would join a minute group of six teams from a 95 team sample to do so.Only six out of 95 have failed to reach .500 by season’s end. Does it happen? Sure. Is it rare? Hell yeah.
And that’s supported out this season too. This year, 15 teams have a positive run differential and only the Mets are under .500. No other team is fewer than three games over, with the Royals at 46-43.
According to the research, “at the exact midpoint of the season (81 games), Pythagorean projection correlates with winning percentage [better than] actual winning percentage [.]” The Mets will probably play like a .500 team from here on out … but this, of course, is no consolation to a team that is presently 45-50. Going .500 from here on out would only result in around 80 wins.
At the end of the day, the gap between what the Mets record is and what the Mets record should be (given their true talent level) can be explained almost entirely by their record in one-run games, in which the Mets are 12-20. Stop me if you’ve heard this before: if the Mets were 16-16 in one-run games, they would be over .500 — or what their run differential says they should be.
I’ve heard all the arguments against run differential and refusing to blame their record in one-run games for the difference, but there is one that seems to have the most traction among the anti-stat crowd:
“Hey Brian, the Mets aren’t unlucky in one-run games, they’re just bad. Good teams win those one-run games. That’s what makes them good teams.”
Well, not exactly. Yes, it is true that great teams have better records in one run games (but maybe not by as much as you think), but the year-to-year records in one run games deviate widely from what you might expect given such a small sample of those games. Look no further than our own Mets!
The 2013 Mets were worse than the 2014 Mets – why did they succeed in one run games? How about the 2008 Mets, who were excellent – why did they fail? How come the best team in baseball right now is barely over .500 in those games? Every team in the NL West is within one game of .500 in one run games … except the lowly Padres, who at 10 games below .500 had a fantastic 17-10 record in one run games.
Sandy Alderson is right. This team is better than last year’s team. The 2013 Mets scored only 619 runs and allowed 684, and this year’s team is better from top to bottom, as we pointed out in our season preview. The results so far, record aside, are good, as this year’s squad is on pace to score 635 runs but allow only 630 — a 70 run improvement.
So when Alderson says that he’s happy with the team, and he’s happy with the run differential, he is not simply buying time or deflecting criticism (although the statements about waiting for the end of the homestand to determine whether or not the Mets should be buyers or sellers is most certainly fictional). He’s making a true statement and showing patience with this club’s turn around.
At some point, you are what your record says you are. But not yet.
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