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The Patriots Really Do Own The Second Half Of The Season

It’s no secret the New England Patriots have been the NFL’s dominant franchise over the past decade-plus. In addition to three Super Bowl victories and five AFC championships, New England has 21 more regular-season wins than any other team since 2001, when Tom Brady became the team’s starting quarterback. The Patriots also have by far the league’s top point differential over that same span.

Achieving those marks has required that New England be very good, but also consistently better than expected. Based on the pregame Elo ratings of the Patriots and their opponents — which theoretically take into account how much talent each team possesses — one would have expected the Patriots to win about 147 of their 218 regular-season games over the 2001-2014 span. Instead, they’ve won 166, a 19-game gap that represents the biggest overachievement in the league.

One of the common aphorisms about New England under Brady and head coach Bill Belichick is they get stronger as the season goes on, which sounds like a convenient narrative to fit any late-season Pats win. But the data backs this up; the Patriots really do outperform expectations at a particularly high rate in the second half of the season. Using the same exercise as above, 14 of those 19 extra wins came then.

In fact, that’s probably understating how much better than their expected baseline the Patriots have been late in seasons. As a team performs better, its Elo rating improves. Elo ratings are supposed to be calibrated to avoid autocorrelation — the tendency for a successful team’s rating to inflate over time because it was not set properly in the first place — and for the whole of the league, this is true. But in New England’s case, its performances are even more pronounced when you freeze its ratings as it was going into the second halves of its seasons.

Using only those “frozen” Elo ratings to generate win probabilities for all second-half games since 2001, the Patriots have won at a rate 14.9 percentage points greater than expected. That’s not only the best rate in the NFL, but it’s double the distance from average (zero percentage points) as the second-ranked team, the Philadelphia Eagles. New England’s second-half overachievement is about 2.4 standard deviations better than average — enough for us to take notice and acknowledge a late-season phenomenon in Foxborough.

The Patriots are usually a tough matchup no matter when a team faces them. But Sunday’s convincing win over the Indianapolis Colts (a game in which Elo had New England as the slimmest of favorites at 52 percent) was just the latest example of the team saving its best performances for the latter stage of the season.

Neil Paine was the acting sports editor at FiveThirtyEight.