After Thursday night’s two-hour special on the NFL Network, we now know exactly what every NFL team’s schedule looks like for the upcoming season. But what we don’t know is how hard any of those schedules will be.
Every year when the schedules are released, NFL analysts ritually compare the strength of the 32 teams’ slates. And every year, they do it the one way we know doesn’t work.
This year is no exception: Analysts are adding up last year’s wins and losses for each team’s 2018 opponents. That approach might make sense if we had no data about how NFL teams perform from year to year — but we have an awful lot, and it says that NFL win-loss records are significantly influenced by luck and are a terrible predictor of themselves.
Twelve years ago, Doug Drinen of Sports-Reference.com saw the annual crop of strength-of-schedule articles spring up and decided to test their merit. He compared NFL team records from the prior year (Year N) with the year before that (Year N-1) and their opponents’ win percentage from Year N-1, and he repeated the process all the way back to 1990.
Drinen found that prior-year wins by a team’s opponents are “essentially irrelevant” to following-year success — and while how well the other team plays absolutely matters when toe meets leather, “these strength-of-schedule estimates that are being thrown around right now seem to have no role at all in determining teams’ (upcoming year) records.”
In a league where about half the teams that make the playoffs in any given year miss them the following season (a whopping eight 2016 playoff teams missed the cut in 2017), assuming every team’s record will remain the same never really made any sense.
But there is a stat that does correlate with upcoming-season wins: Pythagorean wins, based on points scored and points allowed rather than win-loss record. Developed for baseball by Bill James and modified for other sports by current Houston Rockets GM Daryl Morey, this equation is where Pro-Football-Reference.com’s “expected wins” number comes from. In a 2007 blog post, Drinen found that this stat significantly correlates with next-season wins.
If we compare actual wins to expected wins for 2017, we see which teams are most likely to improve in 2018 and which are most likely to regress.
As we wrote before the season, going 0-16 takes not just terrible talent but also terrible luck — and the 0-16 Cleveland Browns’ 3.3 expected wins point toward a rebound in 2018.
On the other side of the ledger, the Buffalo Bills have the biggest negative gap between the number of games they won and the number of games they’d be expected to win. This isn’t a shock: We also wrote about how the 2017 Bills squad was actually bad.
Here’s how the 32 teams’ 2018 opponent slates stack up in terms of actual 2017 win percentage and expected 2017 win percentage, sorted by the difference between the two:
|team||Opp. Win %||Difficulty Rank||Opp. Win %||Difficulty Rank||Diff|
Though 23 of the 32 teams had a difference of less than 1.5 games between expected wins and actual wins, those small differences add up quickly when using the NFL’s division-based schedules. For example, the Pittsburgh Steelers play the Browns and Ravens twice each. Baltimore joined Cleveland among the five biggest underperformers last season, and the two teams’ combined difference in expected wins adds 9.4 wins to the total for the Steelers’ opponents. It’s no wonder, then, that Pittsburgh had the biggest increase between actual and expected 2018 opponent win percentage, jumping from a 25th-ranked 0.477 to the eighth-strongest, at 0.512.
All four of 2017’s 13-win squads — New England, Philadelphia, Minnesota and Pittsburgh — had expected-win values below 12 according to the Pythagorean method. This gives a boost to the schedules of the non-Minnesota NFC North teams, which are slated to play the AFC East: The hard end of their schedules (Minnesota twice, New England) projects as a little less intimidating, and they also draw overachievers like Buffalo and Miami.
Straight opponent win percentage gives the Packers the hardest projected 2018 schedule, and the Detroit Lions are tied for second-hardest. But using expected wins, they drop to seventh and 15th, respectively.
The team that supplants the Packers with the toughest road is the New Orleans Saints. Their degree of difficulty fell slightly with the change from actual win-loss record to expected wins, but it’s still high enough to capture the top spot.
There’s no model that can account for player age, coaching changes, free agency, the draft or player injuries before they happen. Many teams will defy what 2017’s expected-win value suggests about their 2018 outlook. But history tells us that expected-win values do correlate with what’s going to happen this autumn — and raw win-loss numbers don’t.
CORRECTION (April 20, 2018, 3:17 p.m.): An earlier version of a chart in this article incorrectly identified the Arizona Cardinals as the St. Louis Cardinals.