The so-called “Plexiglass Principle” states that “teams that make a significant leap in their performance (or an aspect thereof) over a given season often give back some of those gains during the following year.” Some of that is common sense: Teams have watched you for a full season and saw what you were doing. Rookies who made a huge impact can now be adjusted to. New coaches’ radical ideas aren’t so radical anymore. But it’s this idea that Nate Silver’s FiveThirtyEight lays on the Eagles’ 2014 season in their NFL preview.
The Grantland piece that introduced the idea mentions the 49ers, Packers, and Bengals as examples of the Plexiglass Principle, since they gained the most wins from 2010 to 2011 (seven for the 49ers, five for the Packers and Bengals). How did those teams fare in 2012? The 49ers did give back two of those wins, but they went to the Super Bowl. The Packers gave back four wins (still improving on 2010) and lost in the divisional round. The Bengals won one more game, and then another in 2013, but still lost in the Wild Card round all of those years. In the 2013 season, the two biggest gainers had very different years: The Colts from 2011 to 2013 won two games and then eleven twice in a row. The Vikings went from three to ten and then back down to five wins.
So, that’s what the nerds think about history and the trends, but what does this all say for the Eagles?
Historically, teams like Philadelphia — which improved by six wins from 2012 to 2013 — declined by an average of 2.6 wins the following season.
The Eagles also fueled their turnaround with one of the NFL’s best turnover margins, especially after Nick Foles took over as primary quarterback in week five. Foles had the third-lowest single-season interception percentage of any passer in NFL history last season. Turnovers and interceptions can be quite fickle, though. Individual interception percentages are notoriously random from season to season, and there’s almost no relationship between a team’s per-game turnover differential from one season to the next.
Foles had a low interception rate as a rookie, so the hope in Philadelphia is that he has a knack for avoiding mistakes. But even so, he’s not liable to repeat last year’s mere two-pick performance, and consequently the Eagles are unlikely to post a gaudy turnover margin again — especially after accounting once more for the Plexiglas Principle.
So, the “average” is a 2.6-win dropoff, which gives the 2014 Eagles an impossible record of 7.4-8.6, which would still probably be enough to win the division. FiveThirtyEight’s Neil Paine continues, saying “a drop-off of some sort may be all but inevitable. Fortunately for the Eagles, though, it’s also hard not to see them making another strong bid for the division title in the NFL’s most meh division — regression be damned.”
The whole thing is worth a read as long as you keep in mind that it doesn’t actually evaluate the Eagles talent, and if you’re in for the joy we get in the misery of others when reading things like this: “If the Redskins are counting on Griffin to duplicate (or exceed) his performance of two years ago, they might need a reality check. It’s very possible that Griffin will never again reach that level of play — and it has little to do with his injury.”
[Kyle: It also doesn’t take in to account radically progressive coaches like Kelly, who has now had more than a year to implement his new style and rid the team of certain players he didn’t want. Trends are great, but they ignore a lot of actual facts. This sort of analysis is better served with political polling data than sports, me thinks. But then again, my last post compared the Phillies to a handjob, so I’m not real scientific. I’d also use the Plexiglass Principle to refer to Jeremy Maclin or, more literally, Plaxico Burress. That seems like a better use of Plexiglass. I’m an idiot. Shut it down.]
h/t reader Becca