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LeBron James Destroyed Our Elo Ratings, But Can He Beat The Warriors Again?

It’s become a rite of spring. Every year — or at least every year since LeBron James returned to the Cleveland Cavaliers — our NBA Elo ratings are skeptical of the Cavs when the playoffs begin. And every year, LeBron and Co. have smashed our poor algorithm to bits.

In 2015, the Cavs entered the playoffs with a lukewarm 1631 Elo rating. That’s perfectly respectable, but the sort of rating you might associate with the Los Angeles Clippers or another 50-something-win team that you’d expect to lose in the second round or the conference finals. Instead, Cleveland reached the NBA Finals, losing to the Golden State Warriors in six competitive games even with a depleted roster.

In 2016, the Cavs had a similarly good-but-not-great Elo rating — 1642 — when the playoffs began. But they blew through the Eastern Conference playoffs before beating the 73-win Warriors to win the NBA title, famously overcoming a 3-1 series deficit along the way. Their Elo rating finished at 1759, ranking them among the top 25 teams of all-time and implying that the system had massively underrated them initially.

This year, Elo had the Cavs pegged lower still when the playoffs began last month. Although the Cavs were our preseason favorite to win the Eastern Conference, they slumped at the end of the regular season — losing 13 of their final 22 games, including their last four — and their Elo rating fell all the way to 1545. That isn’t good; it’s the sort of rating you’d normally associate with a No. 6 seed or some other team you’d expect to lose in the first or second round. Accordingly, the Cavs’ chances of winning the title drifted around in the low-to-mid single digits — variously at 2 percent to 5 percent according to our simulations — as the regular season wound down and the playoffs began.

But the Cavs have gone 12-1 in the playoffs and won by an average score of 117-103. Their Elo rating has climbed by almost 150 points, to 1691. They clinched a return to the finals by beating the Boston Celtics by 33 points on Thursday. It’s been dominating stuff.

So has Elo learned its lesson? Well, maybe not. Cleveland’s chances of winning the finals are just 10 percent according to the more advanced, “Carm-ELO” version of our ratings — and 13 percent according to the simpler, original Elo algorithm. Bookmakers also have the Cavs as underdogs, but not as heavily, implying that they have about a 30 percent chance to beat the Warriors again and repeat as champions.

Giving Cleveland only a 10 percent chance is not the hill I want to die on. Our NBA projections are pretty simple, and sports betting markets are pretty sophisticated. While there are occasional exceptions, I’d usually defer to Vegas in the event of a major disagreement.1 Still, we’ve gotten a lot of questions throughout the playoffs about why Elo hasn’t given the Cavs a better chance. There are basically three reasons — but the one that matters the most right now has nothing to do with the Cavs and everything to do with the Warriors.

Reason No. 1: Elo doesn’t account for teams such as Cleveland finding a higher “gear” in the playoffs. We covered this point extensively before the playoffs began, so I won’t go into too much detail here. Our Elo projections — and most other projection systems — essentially treat regular-season basketball as equivalent to playoff basketball. But LeBron’s teams have a long history of performing at a much higher caliber in the playoffs than in the regular season.

Maybe this is because James and his teammates conserve their energy; there aren’t a lot of high-leverage regular-season games in the Eastern Conference, as evidenced by the fact that the Cavs could play so crappily down the stretch run and still stumble into the No. 2 seed. Maybe it’s because LeBron is a terrific half-court player, and there’s a premium on the half-court game in the playoffs as defenses tighten up. In any event, the assumption that playoff basketball equals regular-season basketball seems to be pretty wrong in the case of the Cavs. This is something we plan on re-evaluating as we retune our NBA models this summer.

Reason No. 2: Elo ratings heavily weight recent performance. That hurt Cleveland before, although it’s starting to help them now. Elo ratings were originally devised for chess, which doesn’t have any such thing as a “season.” Instead, performance continuously fluctuates up and down over time. Our Elo-based sports ratings mostly work the same way.2 The more recent the game, the more heavily it gets weighted.

I’d defend this as being the right assumption to make, in general. The degree to which Elo ratings fluctuate from game to game — which is governed by something called the K-factor — has been tested based on tens of thousands of NBA games. Other things held equal, a game played a week ago ought to tell you more than one played six months ago. Elo can be “smart” about catching cases like the 2014-15 Atlanta Hawks, who started out 40-8 but went 20-14 for the rest of the regular season before being swept by Cleveland in the conference finals.

But for a team whose regular-season performance doesn’t tell you much about how they’re going to fare in the playoffs (like the Cavaliers), there isn’t much benefit to doubling down on recent play. Cleveland played pretty well in the first half of the regular season, but middlingly — sometimes even poorly — in the second half. Elo put a lot of emphasis on that late-season slump as the playoffs approached, and that made it more skeptical of the Cavs.

Elo’s philosophy of rapidly adjusting its ratings is benefiting the Cavaliers now, however. Because of their dominance in the playoffs, the Cavs’ current Elo rating has rebounded. Their 1691 is the highest Elo rating they’ve had since Dec. 25, when they were at 1692 and had a 23-6 record after beating the Warriors.

That’s a very good Elo rating. Since the ABA-NBA merger in the 1976-77 season, the average NBA Finals participant has entered the finals with a rating of 1695. So Elo is saying that despite their regular-season struggles, the Cavs are every bit as strong as the typical conference champion.

The Cavaliers are great … but still a big underdog
YEAR
FAVORITE
ELO
WIN PROB.
WON
UNDERDOG
ELO
WIN PROB.
WON
1967 76ers* 1745 92% Warriors 1541 8%
1971 Bucks* 1704 91 Wizards 1507 9
1972 Lakers* 1738 90 Knicks 1555 10
2001 Lakers* 1768 89 76ers 1592 11
1986 Celtics* 1807 88 Rockets 1640 12
2017 Warriors* 1850 87 Cavaliers 1691 13
1963 Celtics* 1677 85 Lakers 1533 15
1996 Bulls* 1832 84 SuperSonics 1695 16
1949 Lakers* 1625 84 Capitols 1490 16
1959 Celtics* 1643 82 Lakers 1514 18
2003 Spurs* 1746 81 Nets 1624 19
1974 Bucks* 1709 80 Celtics 1592 20
2002 Lakers* 1717 80 Nets 1601 20
1999 Spurs* 1745 80 Knicks 1631 20
1962 Celtics* 1669 80 Lakers 1557 20
1960 Celtics* 1676 78 Hawks 1575 22
1950 Lakers 1727 77 76ers* 1597 23
1961 Celtics* 1669 77 Hawks 1571 23
1981 Celtics* 1668 76 Rockets 1573 24
2014 Spurs* 1730 76 Heat 1638 24
1966 Celtics* 1650 76 Lakers 1558 24
2015 Warriors* 1802 75 Cavaliers 1712 25
1957 Celtics* 1630 75 Hawks 1541 25
1965 Celtics* 1653 75 Lakers 1565 25
1956 Warriors* 1617 75 Pistons 1529 25
1975 Bullets* 1659 75 Warriors 1571 25
1951 Royals* 1615 74 Knicks 1531 26
1955 Nationals* 1632 73 Pistons 1551 27
2006 Mavericks* 1717 73 Heat 1637 27
1993 Bulls 1741 73 Suns* 1634 27
1987 Lakers* 1738 72 Celtics 1661 28
1984 Celtics* 1706 72 Lakers 1633 28
1983 76ers* 1707 71 Lakers 1638 29
1964 Celtics* 1669 70 Warriors 1602 30
2016 Warriors* 1790 70 Cavaliers 1725 30
2007 Spurs* 1705 70 Cavaliers 1641 30
1989 Pistons* 1763 69 Lakers 1701 31
2009 Lakers* 1760 68 Magic 1703 32
2000 Lakers* 1699 68 Pacers 1643 32
1991 Bulls* 1750 67 Lakers 1697 33
1952 Lakers* 1646 67 Knicks 1594 33
2012 Thunder* 1737 67 Heat 1686 33
1997 Bulls* 1799 66 Jazz 1751 34
1970 Knicks* 1595 66 Lakers 1549 34
2005 Spurs* 1716 66 Pistons 1670 34
2013 Heat* 1755 65 Spurs 1711 35
1958 Celtics* 1603 65 Hawks 1559 35
1992 Bulls* 1742 64 Trail Blazers 1702 36
1980 Lakers* 1712 62 76ers 1681 38
1954 Nationals 1666 61 Lakers* 1607 39
1990 Pistons* 1688 60 Trail Blazers 1663 40
1985 Lakers 1752 60 Celtics* 1697 40
2008 Lakers 1737 59 Celtics* 1685 41
1978 SuperSonics* 1610 59 Bullets 1590 41
1973 Lakers* 1667 59 Knicks 1649 41
2004 Lakers* 1698 58 Pistons 1682 42
1969 Lakers* 1614 58 Celtics 1598 42
1976 Celtics* 1558 57 Suns 1544 43
1982 76ers* 1699 57 Lakers 1686 43
2010 Lakers* 1686 57 Celtics 1674 43
1979 SuperSonics 1620 57 Bullets* 1577 43
1994 Rockets* 1663 56 Knicks 1655 44
1968 Celtics* 1594 56 Lakers 1586 44
2011 Heat* 1721 55 Mavericks 1717 45
1988 Pistons 1692 55 Lakers* 1658 45
1998 Jazz* 1762 54 Bulls 1761 46
1995 Magic* 1628 52 Rockets 1635 48
1948 Warriors* 1491 52 Bullets 1500 48
1947 Warriors* 1423 52 Stags 1432 48
1977 76ers* 1615 51 Trail Blazers 1624 49
1953 Lakers* 1632 51 Knicks 1641 49

* Home-court advantage.
Elo ratings are for each NBA Finals team as they entered the series.

There’s just one big problem for Cleveland: Golden State.

Reason No. 3: Elo thinks the Warriors are insanely great — one of the two best teams ever, along with the 1995-96 Bulls.

The Warriors’ current Elo rating is 1850. That’s the highest rating a team has held upon entering the NBA Finals. And it’s the second-highest rating a team has had at any point in the regular season or playoffs; the 1995-96 Chicago Bulls peaked at a rating of 1853 after sweeping the first three games of the finals.3 It’s higher than the peak rating of last season’s 73-win Warriors, who topped out at 1839 after starting out the regular season 24-0.

We’ll be publishing a deeper dive on the Warriors next week, but Elo’s affection for them isn’t hard to explain. They’re 27-1 over their last 28 games. That includes a 12-0 record in the playoffs and an average margin of victory of more than 16 points, which is the best playoff scoring margin of all time. And they’ve done all of this in the Western Conference, which is still a lot deeper than the East.4 The Warriors are making it look so easy that they may even be underrated by the “eye test,” which tends to reward teams that triumph in the face of adversity. Other than in Game 1 of the Western Conference finals, the Warriors haven’t faced much adversity because they haven’t let their opponents get close.

PER GAME PLAYOFF AVERAGES
YEAR TEAM W-L POINTS SCORED POINTS ALLOWED SCORING MARGIN
2017 Warriors 12-0 118.3 102.0 +16.3
1971 Bucks 12-2 109.1 94.6 +14.5
2017 Cavaliers 12-1 116.8 103.2 +13.6
2001 Lakers 15-1 103.4 90.6 +12.8
1991 Bulls 15-2 103.9 92.2 +11.7
1961 Celtics 8-2 120.7 109.1 +11.6
1987 Lakers 15-3 120.6 109.2 +11.4
1996 Bulls 15-3 97.4 86.8 +10.6
1986 Celtics 15-3 114.4 104.1 +10.3
1985 Lakers 15-4 126.3 116.2 +10.2
The Warriors have dominated the playoffs like no one before them

Minimum 8 playoff games played.

Source: Basketball-reference.com

To put this in perspective, suppose you took an indisputably great team like the 1986-87 Los Angeles Lakers, who went 65-17 in the regular season and entered the NBA Finals with an Elo rating of 1738. Elo would have given the Lakers only a 20 percent chance to win a seven-game series over the Warriors, assuming that the Warriors had home-court advantage (as they will against the Cavs). Compared with that, the Cavaliers’ 10 percent or 13 percent chance doesn’t seem so bad. Still, I’d put a few dimes down on LeBron at Elo’s odds.

CORRECTION (May 30, 4:05 p.m.): An earlier version of a table in this story gave an incorrect winner for the 1951 NBA Finals. It was the Rochester Royals, not the New York Knicks.

Footnotes

  1. I wouldn’t say that of political betting markets, which aren’t as sophisticated and have a bad track record in recent years compared with simple polling averages.

  2. With some exceptions: Regular Elo ratings revert each team’s rating partway toward the league average at the start of each regular season. And the Carm-ELO version of our ratings start each team out with an initial rating each season based on our player projections.

  3. The Bulls then lost Games 4 and 5 before recovering to win the title in Game 6, finishing with an Elo rating of 1823.

  4. True, Golden State benefited from a playoff injury to the San Antonio Spurs’ Kawhi Leonard — although the Cavs were helped by injuries to the Toronto Raptors’ Kyle Lowry and the Celtics’ Isaiah Thomas.

Nate Silver is the founder and editor in chief of FiveThirtyEight.

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