lunes, 20 de junio de 2016

Analysis of the NBA Coach of the Year Award: a comparison between the official voting and objective techniques

Authors: Julio del Corral (@jdelcorraltm) and Andrés Maroto (@jazzandmar)

Steve Kerr won the NBA Coach of the Year Award last 26th of April. 130 media members from USA and Canada, that regularly cover the North American basketball tournament, were involved in the voting. The coach of Golden State Warriors did not receive the award last year when he led the Californian franchise to win the tournament and achieved the highest number of victories that season. However, he received the award this year after Golden State Warriors set the NBA regular-season record of victories of all times (73-9), surpassing the 72-victory Chicago Bulls from the 1995-96 season. In fact, Kerr played for Phil Jackson back then. Kerr, who is the third Warriors’ coach achieving this award (after Alex Hannum and Don Nelson), will have to share the prize with his assistant coach Luke Walton. The team was led for the first 43 games (39-4) by Walton, as Kerr was recovering from back surgery.
Kerr received a total of 381 points (64 first-place votes), which is only 46 points ahead of the runner-up, Terry Stotts, head coach of Portland Trail Blazers. Stotts qualified the Portland’s franchise for the play-offs against all odds in the 5th West ranking position. Portland is actually fighting a spot in the West final against the Kerr’s Warriors these days. Gregg Popovich (3rd) from San Antonio Spurs, Steve Clifford (4th) from Charlotte Hornets; and Dwane Casey (5th) from Toronto Raptors completed the list.
Previous research shows that this sort of award usually goes to the coaches from the strongest teams not only in the NBA but also in other sports (e.g., soccer). Nonetheless, coaches that are able to obtain a better performance by optimizing their resources and squads should be awarded. During recent years, we have published similar posts analyzing the efficiency of NBA coaches since 1993. For that purpose, we evaluate objectively the performance of each coach comparing their results with those expected from betting odds. The probability of winning each game is implicit in these odds and allows us to calculate the probability function of the number of victories in a season for each team and coach.
The following table shows the results for this season:
Team
Coach
Efficiency
Victories
Eff. Ranking
NBA Ranking
Golden State Warriors 
Steve Kerr
0.99
73
1
1
Toronto Raptors 
Dwane Casey
0.96
56
2
4
San Antonio Spurs 
Gregg Popovich
0.93
67
3
2
Charlotte Hornets 
Steve Clifford
0.93
48
4
10
Portland Trail Blazers 
Terry Stotts
0.89
44
5
12
Miami Heat 
Eric Spoelstra
0.81
48
6
7
Los Angeles Clippers 
Doc Rivers
0.81
53
7
6
Denver Nuggets
Michael Malone
0.78
33
8
22
Dallas Mavericks
Rick Carlisle
0.78
42
9
14
Memphis Grizzlies
Dave Joerger
0.72
42
10
15
Detroit Pistons
Stan Van Gundy
0.69
44
11
13
Washington Wizards 
Randy Wittman
0.65
41
12
17
Boston Celtics 
Brad Stevens
0.56
48
13
9
Orlando Magic 
Scott Skiles
0.52
35
14
20
Indiana Pacers 
Frank Vogel
0.48
45
15
11
Chicago Bulls 
Fred Hoiberg
0.47
42
16
16
Milwaukee Bucks
Jason Kidd
0.47
33
17
23
New York Knicks
Derek Fisher / Kurt Rambis
0.44
32
18
24
Cleveland Cavaliers
David Blatt / Tyronn Lue
0.43
57
19
3
Sacramento Kings 
George Karl
0.37
33
20
21
Minnesota Timberwolves 
Sam Mitchell
0.35
29
21
26
Atlanta Hawks 
Mike Budenholzer
0.34
48
22
8
New Orleans Pelicans
Alvin Gentry
0.29
30
23
25
Utah Jazz
Quin Snyder
0.27
40
24
19
Brooklyn Nets
Lionel Hollins / Tony Brown
0.27
21
25
28
Los Angeles Lakers 
Byron Scott
0.23
17
26
29
Oklahoma City Thunder 
Billy Donovan
0.20
55
27
5
Houston Rockets 
Kevin McHale / JB Bickerstaff
0.18
41
28
18
Phoenix Suns 
Jeff Hornacek / Earl Watson
0.04
23
29
27
Philadelphia 76ers
Brett Brown
0.03
10
30
30

Our results show that the first position is the same either with the official ranking or using our methodology. Other coaches also hold a pretty accurate efficiency-ranking of victories relationship (not only coaches from the higher ranked teams, e.g., Casey, Popovich, Spoelstra or Rivers, but also coaches from the lower ranked teams, e.g., Hoiberg, Karl, Gentry, Scott or Hornacek). This method also identifies the worst coach of the year, Brett Brown from Philadelphia 76ers. In general, the correlation coefficient between both measures is 64%.
There is little discussion among fans and media experts about the best coaches this season as Kerr, Stotts and Popovich showed an outstanding performance (apart from highlighting the performance of Walton leading the Warriors in the first games of the season). In fact, all of them might still improve their numbers as they are coaching their teams in the conference semifinals at the moment.
Nonetheless, we can observe significant differences in other teams. Steve Clifford (Charlotte Hornets) would be the 4th best coach of the year with a higher efficiency than Terry Stotts. Other coaches underrated according to the final number of victories are Michael Malone (Denver Nuggets) or Rick Carlisle (Dallas Mavericks). On contrary, coaches whose teams are still competing in the conference semifinals, i.e., Tyronn Lue, who substituted David Blatt in the second half season, would go down to the 19th position of the ranking, even though Cleveland Cavaliers finished in the 3rd position according to the ranking of victories. In a similar way, Billy Donovan, Oklahoma City Thunder coach (5th position), would go down to the 27th position in terms of efficiency, or even Mike Budenholzer, Atlanta Hawks coach, who won the NBA Southeast Division last year.
Finally, another interesting point is that the change of the coach has not resulted in great improvements in general as all teams that did it (Knicks, Nets, Lakers, Cavs, Rockets or Suns) are below the efficiency average (i.e., 53%).
We think these awards should not only be based on the total number of victories at the end of the season. Our methodology has limitations but it is a good starting point for the development of an objective ranking, which seems to be in line with NBA fans opinions. Because of all this, the voting system could be substituted for some kind of scientific objective indicator (see the one proposed here) to award the official prizes at the end of the season.

Special thanks to Carlos Gómez González

Follow us on Twitter: @jdelcorraltm @jazzandmar

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