Wait, the Cubs aren’t projected to be the best team in 2017? Yep, you read that correctly. Not only are the world champs not projected to be the best, but PECOTA — one of the most accurate projection systems known to man — believes the Cubs will win 91 games and finish with the fourth-best record, behind the Dodgers (98), Astros (93), and Indians (92).
How does a team with a 108-win Pythagorean expectation, 107-win BaseRun total, and 103 actual wins in 2016 not follow up with the best projection for 2017?
The answer to the question is multifaceted, but to understand a model’s strengths and limitations, we first need to know its general methodology. Don’t worry, we don’t have to dive into the advanced statistical processes to grasp the model’s conventional wisdom.
How PECOTA Works
PECOTA projects a current player by matching him to a similar historical player from a pool of about 20,000 individual seasons. For prospects or younger players still in the baby-stage of their careers, PECOTA instead pulls from approximately 15,000 minor league player options. Matches are based on production metrics (batting average, ISO, walks, etc. for hitters; strikeouts, ground ball rate, etc. for pitchers), career length, body type, and position.
For you math nerds, Nate Silver developed PECOTA by using nearest neighbor analysis and looking at three-season window buckets.
PECOTA naturally ignores unquantifiable behavior traits and relevant peripherals such as contact rate, o-swing rate, etc., all of which are prone to dramatic age-dependent changes.
How PECOTA Performs
So does PECOTA actually work? Yes, compared to a team’s previous year, it does a much better job at projecting wins, according to Russell Carlton’s findings. Further, PECOTA projects wOBA more accurately than any other public projection system. It is arguably the most respected system out there.
Nevertheless, PECOTA explains only about 17% of a 90-plus-win team’s total. That means it doesn’t capture about 83% of what makes the best teams good. More specifically, this particular system is unable to quantify a vast majority of what makes the Cubs good. Yes, even one of the most accurate projection systems mankind has created must still genuflect before the baseball gods.
How PECOTA Projects The Cubs
I see a few things that make you go “hmmmm” in these projections. First, I think Willson Contreras’s comps are slightly skewed because PECOTA matches him using minor league numbers. That means he is going to be matched with guys who struck out significantly less because Contreras himself struck out significantly less in the minors. We saw how he made some adjustments at the big league level, generally sacrificing contact for power.
Likewise, Addison Russell improved his contact rate, yet PECOTA matches him using players who struck out significantly more. Finally, we already know isolated metrics can’t handle Kyle Hendricks, so it’s no surprise PECOTA projects only 2.2 wins for the 2016 Cy Young candidate.
PECOTA is my favorite projection system, but I try to be careful not to over-interpret its results, especially since the model only captures a small piece of the “what makes a player/team good” pie. This fact, however, won’t stop me from laughing at the Cardinals’ projected 76-86 record.
I like incorporating these projections into plate-discipline trends and mechanical adjustment observations. For example, because of Addy’s contact improvement, I think PECOTA system might be missing out on Russell in particular.
Remember, the Cubs punched PECOTA in the face by having a 108-win Pythag mark, 16 more than what the model thought they would win in 2016. The beauty of baseball is that it is both metaphorically and literally dirty. As Carlton so eloquently described:
We actually have no idea what to believe, at least if we’re being honest with ourselves and taking a sober look at our numbers. We have a crude and cloudy crystal ball and when we try to tune into what’s going to happen in October, we keep getting interference from the golf channel.