A New Method for Ranking Total Driving Performance on the PGA Tour

Abstract

The Professional Golf Association Tour (PGA Tour) currently ranks its
players according to their overall Total Driving performance by adding
together individual ranks for their average driving distance and for their
driving accuracy percentage. However, this widely used and reported measure
is inappropriate because it is based upon the addition of two ordinal-scaled
measures in which the underlying differences between successive ranks
are not equal. In this paper, we propose a new method for ranking golfers
in terms of their overall driving performance. The method eliminates the
drawbacks of previously reported measures, including the one used by the
PGA Tour. Using the new methodology, we re-rank all PGA Tour golfers for
the 2005 season and compare these ranks to the “official” ranks reported
by the PGA Tour. In some cases, large differences in players’ rankings
existed. The reasons for these differences are then discussed.

Introduction

In recent years, numerous statistical analyses have been conducted in
an attempt to assess the relative importance of various shot-making skills
on overall performance on the PGA Tour and among amateur golfers (Shmanske,
2000; Dorsel and Rotunda, 2001; Engelhardt, 1997 and 2002; Callan and
Thomas, 2004 and 2006; and Wiseman and Chatterjee, 2006). While most of
the measures that have been used in these analyses have been well-defined
and widely accepted, there is one performance statistic, “Total Driving,”
that has not been well-defined. This particular statistic, which combines
a golfer’s (i) average driving distance and his/her (ii) driving accuracy
percentage, has been operationally defined in numerous ways, but no methodologically
sound measure has emerged to date. This includes the measure now being
used by the PGA Tour.

In this paper, the authors propose a new statistical measure based upon
standardized z-scores for ranking golfers according to Total Driving performance.
This new measure eliminates the methodological drawbacks of previously
developed measures by re-ranking PGA Tour golfers on their Total Driving
performance during the 2005 season and comparing these rankings to the
“official” PGA Tour rankings for that season.

The evolving nature of the relationship that has existed between driving
distance and driving accuracy on the PGA Tour over the last sixteen years
(1990-2005) was examined. Then, alternative ranking methods that have
been proposed and the necessity of and the rationale for a new composite
measure of Total Driving performance were discussed. Following this, the
new measure can be applied to the 2005 PGA Tour season. These new rankings
dramatically alter the previous ranking of many golfers on the tour. The
reasons for the differences in rankings will be explored.

Distance and Accuracy on the PGA Tour: 1990-2005

The average driving distances and the driving accuracy percentages have
changed significantly since 1990, with the largest changes taking place
in recent years. This is shown in Table 1. The average driving distances
have increased every year since 1993 and these increases have been relatively
steady on a year-by-year basis, except in 2001 and 2003, when the increases
were significantly higher. We surmise that technological improvements
in golf balls and equipment are likely to have played a part in these
two years.

A similar trend did not exist for the driving accuracy percentage. Here,
the accuracy percentage steadily increased from 1990 to 1995, and then
remained relatively stable over the next six-year period, only to decline
dramatically in the last few years. This dramatic decline occurred at
the same time that the average driving distance substantially increased.
In fact, during the 2005 PGA Tour season, the average driving distance
was at its sixteen year high of 288.6 yards and the driving accuracy percentage
was at its sixteen year low at 62.8%.

The negative relationship between a golfer’s average driving distance
and driving accuracy percentage increased in strength over this sixteen
year period. As indicated in Table 1, the strength of the relationship
has grown in recent years and it reached its highest level in 2005, when
the correlation between the two measures was -.679.

Current Measures of Total Driving Performance

Ranking golfers on each of the two driving measures presents no problems.
Driving distance is simply defined as the average number of yards per
measured drive. For each golfer, these drives are measured on two holes
per round. Driving accuracy is the percentage of all drives that come
to rest in the fairway. However, the PGA Tour and others (for example,
Engelhardt, 1997) have indicated the need for a single measure that takes
into account both the driving accuracy percentage and the average driving
distance. Numerous researchers have attempted to obtain such a measure;
unfortunately all of the measures that have been proposed have had methodological
flaws associated with them.

The most widely used measure is the one used by the PGA Tour. It is obtained
by adding together the individual ranks of a golfer on each of the two
measures and then obtaining a final overall ranking based upon the total
score. That is, for example, a golfer who was ranked 32nd in driving distance
and 42nd in driving accuracy percentage would have a total score of 32+42=74.
The PGA Tour would rank such a golfer higher than another golfer who ranked,
for example, 25th in average driving distance and 60th in driving accuracy
percentage, since the former summated score of 74 is lower than the latter
summated score of 85.

Such an approach is flawed despite its widespread use and acceptance.
The major flaw is that the level of measurement of each of these two rankings
(driving distance and driving accuracy) is at the ordinal level and, as
such, it does not take into account the underlying differences in distances
or in driving accuracy percentages. Stated differently, while the differences
in successive ranks remain the same, the corresponding differences in
distance and accuracy are not equal. Thus, it is not possible to add the
distance and accuracy ranks directly, without loss or distortion of the
underlying information.

Davidson and Templin (1986) suggested a somewhat different approach.
They proposed a measure which first divided all PGA Tour players into
three groups based upon their average driving distance. They then made
a similar classification based upon the driving accuracy percentage. The
three groups were coded as 1 (top one-third), 2 (middle one-third), and
3 (bottom one-third). To arrive at a measure of Total Driving performance,
the researchers multiplied the individual coded scores of each golfer.
The larger the score, which ranged from 1 to 9, the better the performance.
The authors used this new measure in a multiple regression analysis in
an attempt to isolate the effects of driving on overall scoring performance.

This measure was questioned by Belkin et al. (1994) because no evidence
was provided to support the construct validity of the measure and because
of the multiplication of the individual codes at the ordinal level of
measurement.

More recently, Wiseman and Chatterjee (2006) proposed a multiplicative
measure of Total Driving which ranked golfers according to the product
of their average driving distances and their driving accuracy percentages.
Essentially, this measure reduced golfers’ average driving distances by
the proportion of times their drives did not land on the fairway. Thus,
a golfer who had an average driving distance of 300 yards and an accuracy
percentage of 60% would be ranked lower than another golfer who had an
average driving distance of 280 yards and an accuracy percentage of 70%,
since 300(.60) =180 < 280(.70)=196. This measure was found to be highly
correlated with the PGA Tour measure, but subsequent analyses revealed
that it was also flawed because it gave far greater weight to driving
accuracy than it did to driving distance. However, unlike the two previously
discussed measures, it was operationally sound in that it was appropriate
to multiply the two quantities together.

In summary, different measures for Total Driving performance that have
been used are all flawed, and it is difficult to justify any of them as
an appropriate measure. In the next section of this paper, a new method
for ranking golfers that have none of the drawbacks of the previously
discussed measures will be explained.

A New Measure for Ranking Total Driving Performance

Both average driving distance and the driving accuracy percentage are
ratio-scaled data. To combine these two measures into a single overall
measure of Total Driving performance, the measure we propose is based
upon two statistically independent standardized z-scores, one for driving
distance, and the other for driving accuracy given driving distance.

In proposing such a measure, if the distance and accuracy measures are
statistically independent and they are viewed as being of equal importance
in driving performance, then it would be reasonable to compute the standardized
z-score of each measure, and then to add these z-scores to arrive at an
overall score. However, this approach does not seem reasonable in the
present situation because (i) there is a strong negative correlation between
driving distance and driving accuracy, and (ii) driving distance is the
primary factor in determining accuracy, rather than the other way around
(driving distance is primarily a function of a player’s physical strength
and athletic ability). With this reasoning, we propose the following as
a composite score of Total Driving:

Zsum = ZDD + ZDA|DD

where:

ZDD = Standardized z-score of
driving distance, and

ZDA|DD = Standardized z-score
of driving accuracy given driving distance.

To compute ZDD for a player, we subtract the average driving
distance for all players, µDD, from the given player’s
average driving distance, DD, and divide the result by the standard deviation
of average driving distances, σDD. This is expressed
as:

ZDD= DD-µDD
σDA|DD

Computation of ZDA|DD is a somewhat more involved procedure.
We need to determine the mean or expected accuracy percentage of all golfers
who drove the ball a specified average distance, DD, as well as the standard
deviation of the driving accuracy percentages given the specified average
distance, DD. The formulas for these are:

µDA|DD = ρσDA((DD-µDD)/σDD),
and σDA|DD = √((1-ρ2DA2

where ρ is the correlation coefficient between distance and accuracy.
The conditional standardized z-score of driving accuracy given driving
distance is then computed using the following formula:

ZDA|DD = (DA – µDA|DD) / √((1-ρ2DA2.

Statistical theory about bivariate normal distributions tells us that
z-scores for distance and accuracy, ZDD and ZDA|DD,
both have a mean of 0.0 and a standard deviation of 1.0. Further, the
conditional z-score for accuracy given distance, ZDA|DD, is
statistically independent of the z-score for driving distance, ZDD.

Because the two standardized z-score measures are statistically independent,
and because ZDA|DD is an indicator of accuracy after taking
distance into account, they can be added together to obtain an overall
summated z-score for overall driving performance. The higher the overall
value of Zsum = ZDD + ZDA|DD, the better
the overall performance.

The authors will discuss in greater detail the application of this approach
for ranking golfers based upon their Total Driving performance in the
2005 PGA Tour season.

Application to the 2005 PGA Tour Season

In 2005, there were 202 golfers on the PGA Tour. Detailed statistical
data for these players can be found on the PGA Tour’s website (www.pgatour.com).
Anderson Darling’s (AD) test was used to determine if driving distance
has a normal distribution. With this test, we reject the null hypothesis
that the data came from a normal distribution if the AD statistic is very
large, or equivalently, if the p-value is smaller than a chosen level
of significance (usually 0.05 or 5% level of significance). Our data show
that the AD statistic was 0.367, which is small, and the p-value is 0.429,
which is larger than the 5% level of significance. Therefore, we do not
reject the hypothesis that the data came from a normal distribution.

Similarly, we used the AD statistic to test whether the driving accuracy
percentage variable was Normally distributed. The AD test produced a test
statistic of 0.350 with a p-value of 0.471. As a result, we do not reject
the hypothesis that the driving accuracy percentages are Normally distributed.
Given these results, we concluded that the joint distribution of driving
accuracy and driving distance can be represented by a bivariate Normal
distribution, with a correlation coefficient of ρ = -.679 between
the two variables.

Next, the authors computed the values of Zsum as the Total
Driving scores, and ranked these values in descending order. The scores
for the top forty players in the resulting ordering, together with the
corresponding PGA Tour ranks, are shown in Table 2.

As it is seen in Table 2, Tiger Woods was the number one ranked golfer
in terms of Total Driving under the proposed method, which stands in sharp
contrast to his rank of 83rd in the PGA Tour rankings. In terms
of average driving distance, Woods was ranked 2nd in 2005 among
202 Tour players with an average driving distance of DD = 316.1 yards.
The top ranked player was Scott Hend, who had an average driving distance
of 318.9 yards. Woods’ average driving accuracy percentage of DA = 54.6%
gave him a PGA Tour ranking of 188th on this measure. The top
ranked player was Jeff Hart with a driving accuracy percentage of 76.0%.
Woods’ two ranks of 2nd and 188th led to his overall
ranking of 83rd for Total Driving based upon the PGA Tour method.

To illustrate the computation of ZDD , ZDA|DD ,
and Zsum for Tiger Woods, in 2005, the average driving distance
among all players was 288.6 yards with a standard deviation of 9.32 yards.
The average for the driving accuracy percentage was 62.8% with a standard
deviation of 5.32%. As noted previously, the correlation between driving
accuracy and driving distance was -.679. Then, the standardized driving
distance z-score for Tiger Woods is:

ZDD = (316.1 – 288.6) / 9.32 = 2.95.

The conditional mean driving accuracy percentage given the average driving
distance of 316.1 yards is:

µDA|DD = 62.8% + (-.679)(5.32%)(2.95)
= 52.1%.

That is, Tiger Woods or any golfer who has an average driving distance
of 316.1 yards would be expected to have a driving accuracy percentage
of 52.1%. Since Woods’ actual driving accuracy percentage for 2005 was
54.6%, his conditional z-score would be equal to:

ZDA|DD = (54.6 – 52.1) / √((1-(-.679)2)(5.32)2)
= .63

By adding the two z-scores for Tiger Woods, an overall Zsum
score of 3.58 is obtained, which is the highest of any of the PGA Tour
players in 2005.

The rationale for Woods’ jump in the rankings can be seen by a closer
examination of the z-scores. His average driving distance of 316.2 yards
far outdistanced all other golfers (except one). His z-score value of
2.95 reflects this large differentiation, whereas previously his ranking
of 2nd did not because it assumed that the distances between
ranks were equal when they were not. Further, his conditional z-score
for driving accuracy is now positive where before it was negative. The
reason for this is because his relatively low driving accuracy percentage
of 54.6% did not reflect at all how far Woods drove the ball. Actually,
for those who drive the ball this far, a driving accuracy percentage approximately
two percentage points lower could be expected. These two factors taken
together accounted for his top ranking.

The Spearman rank correlation between the PGA Tour rankings and the new
rankings was computed to be rs = .90 (p < .001). This
shows that there was a large degree of similarity between the two rankings.
On the other hand, and as illustrated by the case of Tiger Woods, there
were also dramatic differences in some cases. To get a better feel for
the differences, consider the scatterplot of the rankings under the two
methods, which is shown in Figure 1. It is seen that the rankings under
the two methods are generally similar, particularly in the middle range
of rankings, but discernibly less so near the top or the bottom ranges.
Divergence of the rankings at the extremes in this way emphasizes the
effect of the ranking method on the results, which in turn brings the
virtues and flaws of the ranking methods into focus.

Golfers whose rank improved included V. J. Singh, from 38th
to 13th, Davis Love III, from 59th to 11th,
and Brett Wetterich, from 73rd to 4th. Those going
in the opposite direction included Marc Calcavecchia, from 21st
to 45th, Jonathan Kaye, from 23rd to 44th,
and Justin Rose, from 13th to 33rd. Typically, the
reason for a golfer improving rank is because one of the measures was
quite good and the standardized z-scores now reflect this, while the previous
ranking system did not. For those golfers falling in rank, their old ranks
tended to be clustered around many other golfers and their actual differences
in rank did not reflect this closeness. For example, Justin Rose had a
driving accuracy percentage of 63.7%, which gave him a ranking of 81st
among all golfers on this measure. However, fellow competitor Marc Hensby
had a driving accuracy percentage of 62.7%, just one percentage point
less, yet Hensby’s rank of 102nd was 21 ranks below that of
the rank given to Justin Rose.

Summary

The proposed method for ranking golfers according to their Total Driving
skill takes into account the magnitude of the differences that exist between
players on each of the two driving dimensions. The current PGA Tour method
does not. The proposed method also takes into account the strong negative
relationship that exists between driving accuracy and driving distance.
This negative relationship is reflected in the new conditional standardized
z-score. As a result, this new method gives a better overall reflection
of the true Total Driving performance of PGA Tour golfers than does the
current ranking system. Computationally, the proposed method is slightly
more involved than other existing methods, but this is not a significant
factor today.

It should be noted that this methodology can be applied in other areas
in which an overall ranking is desired based on two correlated factors,
which have different units of measurement and thus need to be combined
in some way to provide an overall ranking.

References

Belkin, D.S., Gansneder, B., Pickens, M., Rotella, R. J., & Striegel,
D. (1994) “Predictability and stability of Professional Golf Association
tour statistics.” Perceptual and Motor Skills, 78, 1275-1280.

Callan, S. J. & Thomas, J. M. (2004) “Determinants of success among amateur
golfers: An examination of NCAA Division I male golfers.” The Sports Journal
7, 3 at http://www.thesportjournal.org/2004Journal/Vol7-No3/CallanThomas.asp.

Callan, S. J. & Thomas, J. M. (2006) “Gender, skill and performance in
amateur golf: An examination of NCAA Division I golfers.” The Sports Journal
8, 2 at http://www.thesportjournal.org/2006Journal/Vol9-No3/Callan.asp.

Dorsel, T.N., & Rotunda, R. J. (2001) “Low scores, Top 10 finishes and
big money: An analysis of Professional Golf Association Tour statistics
and how these relate to overall performance.” Perceptual and Motor Skills,
92, 575-585.

Engelhardt, G. M. (1997) “Differences in shot-making skills among high
and low money winners on the PGA Tour.” Perceptual and Motor Skills, 84,
1314.

Engelhardt, G. M. (2002) “Driving distance and driving accuracy equals
total driving:Reply to Dorsel and Rotunda.” Perceptual and Motor Skills
95, 423-424.

Shmanske, S. (2000) “Gender, skill and earnings in Professional Golf.”
Journal of Sports Economics 1(4), 385-400.

Wiseman, F. and Chatterjee, S. (2006) “A comprehensive analysis of golf
performance on the PGA Tour: 1990-2004.” Perceptual and Motor Skills,
102, 109-117.

 

TABLE 1
Driving Distance and Driving Accuracy: 1990-2005

Year Average Driving
distance (yds.)
Driving accuracy
percentage
Correlation between
distance and accuracy
1990 262.7 65.3% -.359
1991 261.4 67.1% -.306
1992 260.4 68.6% -.416
1993 260.2 68.8% -.417
1994 261.9 69.2% -.346
1995 263.4 69.5% -.457
1996 266.4 68.3% -.469
1997 267.6 68.6% -.448
1998 270.5 69.5% -.469
1999 272.5 68.4% -.471
2000 273.2 68.3% -.379
2001 279.4 68.4% -.346
2002 279.8 67.7% -.474
2003 286.6 66.1% -.612
2004 287.2 64.1% -.606
2005 288.6 62.8% -.679

 

Table 2
Revised 2005 PGA Tour Rankings for Total Driving (Top 40 players)

Player Driving
Distance
(yards)
Driving
Accuracy
(%)
Expected
Driving
Accuracy (%)
ZDD ZDA|DD ZSUM Rank PGA
Rank
Woods 316.1 54.6 52.1 2.95 0.63 3.58 1 83
Perry 304.7 63.4 56.6 1.73 1.75 3.48 2 2
Gutschewski 310.5 57.9 54.3 2.35 0.92 3.27 3 54
Wetterich 311.7 56.6 53.8 2.48 0.70 3.18 4 73
Hearn 295.2 68.5 60.2 0.71 2.11 2.82 5 1
Gronberg 301.4 63.2 57.8 1.37 1.37 2.74 6 6
Frazar 301.0 63.5 58.0 1.33 1.41 2.74 7 3
Warren 299.2 64.2 58.7 1.14 1.41 2.55 8 3
Glover 302.2 60.7 57.5 1.46 0.81 2.27 9 26
MacKenzie 300.2 62.1 58.3 1.24 0.97 2.22 10 11
Love III 305.4 57.9 56.3 1.80 0.41 2.21 11 59
Garcia 303.5 59.4 57.0 1.60 0.61 2.21 12 38
Durant 289.2 70.9 62.6 0.06 2.13 2.20 13 5
O’Hair 300.1 61.4 58.3 1.23 0.78 2.02 14 26
Singh 301.1 60.2 58.0 1.34 0.57 1.92 15 38
Long 298.3 62.4 59.0 1.04 0.86 1.90 16 13
Smith 300.8 60.2 58.1 1.31 0.54 1.85 17 44
Hend 318.9 45.4 51.1 3.25 -1.45 1.890 18 107
Hughes 291.3 67.5 61.8 0.29 1.47 1.76 19 7
Stadler 300.1 60.4 58.3 1.23 0.53 1.76 20 50
Allenby 297.7 62.3 59.3 0.98 0.77 1.75 21 20
Mayfair 288.2 69.8 63.0 -0.04 1.75 1.71 22 9
Appleby 300.6 59.3 58.1 1.29 0.29 1.58 23 61
Snyder III 291.8 66.3 61.6 0.34 1.21 1.56 24 8
Purdy 295.2 63.4 60.2 0.71 0.81 1.52 25 15
Brigman 295.5 63.1 60.1 0.74 0.76 1.50 26 18
Bryant 283.2 73.0 64.9 -0.58 2.07 1.49 27 30
Rollins 294.4 63.7 60.6 0.62 0.81 1.43 28 10
Jobe 302.3 57.3 57.5 1.47 -0.05 1.42 29 82
Brehaut 286.6 69.9 63.6 -0.21 1.62 1.40 30 17
Ogilvy 298.0 60.7 59.2 1.01 0.39 1.40 31 54
Henry 297.6 61.0 59.3 0.97 0.43 1.40 32 44
Rose 294.1 63.7 60.7 0.59 0.78 1.37 33 13
Westwood 296.8 61.5 59.6 0.88 0.48 1.36 34 43
Johnson 290.0 66.9 62.3 0.15 1.19 1.34 35 15
Senden 291.0 66.0 61.9 0.26 1.06 1.31 36 11
Mickelson 300.0 58.7 58.4 1.22 0.08 1.30 37 77
Watney 298.9 59.4 58.8 1.11 0.15 1.26 38 68
Trahan 295.8 61.8 60.0 0.77 0.46 1.23 39 33
Pappas 309.4 50.6 54.7 2.23 -1.06 1.17 40 109

Figure 1.
Scatterplot of Revised Rankings Versus PGA Tour Rankings


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