Coauthored
with Fernando Herencia

The
ESPN web has recently published an article where it was provided a
ranking for the NBA coaches of this season. In doing so, they asked a panel of
experts to “rate each team's coach in terms of
their performance in guiding the franchise to overall on-court success, both in
the short and long term”. In the explanation of the methodology by the
ESPN it is said that “there's still virtually no
objective measure to rate the guys who draw up the plays and manage the egos apart
from titles and rings”. It is true that there is not an objective
measure to evaluate the performance in the long term since they are based on
expectations, however it is not true that there is no objective measures to
analyze the coaches’ performance. The most popular is that based in frontier
methods, in which for each coach is attributed in some way the quality of his
rooster and subsequently it is evaluated the difference between the actual
results and the best results possible for his squad. The lower the difference
between them the better the coach performance is. This methodology was used to
evaluate NBA coaches´ performance in this
paper from Dave Berri.

Other
alternative to evaluate objectively the coaches’ performance is to compare the
actual results with those expected from betting odds. The probability of the
two possible outcomes in a game (

*i.e.*, local victory and away victory) is embedded in betting odds so that it is enabled to calculate the probability of getting each of the possible number of victories.
Next
graph shows the density function of victories for Miami Heat and Charlotte
Bobcats within this season till their matchday 74. It can be seen that the
probability of obtaining less than 40 victories for the Miami Heat is almost
zero. The opposite is true for Charlotte Bobcats. The reason is
straightforward: Miami Heat has a much better rooster than Charlotte Bobcats.

In
order to obtain an objective coach performance measure it can be calculated the
probability of obtain more victories than the actual. Next table shows the
probability of obtain each of the possible number of victories greater than 36
for the Charlotte Bobcats.

As
it can be seen, the probability of obtaining more victories than the actual (36
out of 74) is 2.71%. Then, to calculate an objective measure of the performance
of the team it has to be calculated the inverse of 2.71%, that is 97.3% or 9.73
out of 10.

Next table shows the coaches’ performance using the
methodology described above in the 74 first matches for each team such as the
ratings provided by the ESPN.

As
it can be easily observed several differences arise between both ratings. Particularly,
the coefficient of linear correlation is 63 whereas the coefficient of Spearman
rank correlation is 68%.

The
best five coaches according to ESPN are Gregg Popovich, Tom Thibodeau, Doc Rivers, Erik Spoelstra y Rick
Carlisle. They won five out of the last seven NBA Finals and it is
straightforward that they were important in doing so. However, the performance
of their teams is not as brilliant as expected, especially Indiana Pacers and
Miami Heat.

On
the other hand, Steve Clifford (Charlotte
Bobcats) and Jeff Hornacek (Phoenix Suns) are situated in the top of the
ranking from our methodology but both are not situated so high in the ESPN
rank. Both teams have been two of the positive surprises in the NBA. Charlotte
Bobcats was the second worst team in the NBA last season (2012-2013) while
Phoenix Suns was the second worst team in the Western Conference. Subsequently,
their expectations were rather low. However, both teams are in play-off
positions 8 matches to go. Therefore, it is sensible that both coaches are
leading the ranking.

The
ESPN ratings seem to show some favoritism to big teams such as Miami Heat and
Indiana Pacers. Both teams have very good roosters and it is expected a very
good performance from them. For instance 9 and 10 matches for Miami Heat and
Indiana Pacers respectively have a probability of victory higher than 87% while
playing at home. Thus, even though both teams are leading the East Conference
the number of victories from them is lower than a number to be considered as a
great performance.

Boston
Celtics is other example of sharp difference. Brad
Stevens was ranked 11

^{th}by the ESPN but 27^{th}from ours, but 23 victories seems very few for them. The opposite is true for Mike D’Antoni. Even though Lakers has a very good rooster injuries have decreased a lot the Laker potential. As an example in the first game versus LA Clippers the embedded probability of Laker victory was only 20% playing as local. Hence, even though the Laker season is being awful it is not due to a bad coach performance but to bad luck for injuries.
In
summary, so far the best coaches have been Jeff Hornacek (Phoenix Suns) and
Steve Clifford (Charlotte Bobcats) with a very remarkable 9,73 out of 10 rating
followed by Gregg Popovich (San Antonio Spurs). On the other hand the worst
coaches have been Larry Drew (Milwaukee
Bucks) and John Loyer (Detroit
Pistons).

Hence,
we should carry out this analysis for more seasons in order to get an accurate
ranking of coaches. We are working on it!

Follow
me on twitter: @jdelcorraltm

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