• Analytics Blog
May 5th, 2018
THE PLAYERS Championship is golf's so-called 5th major. This designation is in part driven by the idea that the tournament hosts the strongest field in professional golf. Comprised of the the top 125 players on the previous year's money list, or anyone ranked inside the current top 50 in the world (in addition to a few other select criteria), the field at THE PLAYERS is certainly of major-championship calibre; but is it the strongest in the game?

Measures of field strength can be broadly grouped into two categories. First, measures defined by the quality of the players in the field; and second, measures defined by the difficulty of winning the tournament. In general, these different measures of field strength will correlate strongly; however a relevant omitted variable is the size of the field. There are several tournaments on the PGA TOUR that have very high average player quality, but because they are small fields they are not the most difficult to win (e.g. the 30-man field at The TOUR Championship).

In this article we calculate various measures of field strength (all of which can be grouped into one of the two categories mentioned above) for the 4 major championships, plus THE PLAYERS Championship, for the years 2011-2017. The field sizes of the five tournaments we analyze here are: THE PLAYERS (144), The Masters (90-100), The U.S. Open (156), The British Open (156), and The PGA Championship (156).

The key input to any estimate of field strength is a measure of each golfer's ability at the time of the event. The details on how we estimate golfer ability over time are provided in the first Endnote to this article. Roughly, ability is defined by a golfer's historical adjusted scoring average (with recent performances weighted more heavily). The "adjusted" part accounts for the fact that not all raw scores are equal (e.g. 72 at a U.S. Open is likely better than 72 at PGA West); we adjust scores so that they can be interpreted as relative to the average golfer on the PGA TOUR in the 2017 season. We refer to this as adjusted strokes-gained; it allows us to make fair comparisons of performance across different courses and years. An example for clarity: an adjusted strokes-gained value of +2.3 indicates that the golfer's performance in that round is 2.3 strokes better than what the average PGA TOUR professional from the 2017 season would be expected to shoot in that tournament-round.

In the graph below, we plot the average adjusted strokes-gained on the PGA TOUR for each season from 2011-2017; this indicates how the skill level of an average PGATOUR professional has evolved over the last 7 years. Additionally, we include the average adjusted strokes-gained for the top 5 players in each season. Hover over the data to see the underlying values.
Notes: A strokes-gained value of zero is set to be equal to the average PGA TOUR player in 2017. "Top 5 Avg" represents the average of the players with the 5 highest strokes-gained averages in that year. "PGA TOUR Avg" is the average strokes-gained of a player in a PGA TOUR field in the relevant year. Therefore, by this definition, the more rounds a golfer plays, the more they contribute to the average. To see how we adjust strokes-gained for field strength see the first endnote to this article.
There are two relevant points to take away here. First, the average player quality on the PGA TOUR has been rising over time (if only slightly). Differences in the adjusted strokes-gained measure reflect true differences in skill (i.e. not technology or other superficial changes). Second, notice that on average a Top 5 player on the PGA TOUR is about two strokes per round better than the average professional in a given year.

We define 7 different measures of the strength of a tournament's field. The first two shed light on how difficult it is to win the tournament: with our estimates of each player's skill level we are able to simulate the probability that an average PGA TOUR professional, as well as a Top 5 player, would beat the field (see Endnote 2 for an explanation). The definitions of an average professional and a Top 5 player are specific to each year (values in the first figure are used). Therefore, it makes sense to compare these field strength measures within each year, but not across years. The other field strength measures are related to average player quality: the average skill level of all players in the field (referred to below as "Overall"); the average skill level for the best 25 % of players in the field ("Top 25 %"); and three other "%" terms that are defined anologously. Take some time to explore the table:
Notes: "Average PGATOUR Player" and "Top 5 Player" are defined using the numbers in the first figure of this article (the difference between the two is typically about 2 strokes per round). Win probabilities are obtained by simulation using the entire field plus the additional hypothetical player (PGA average or Top 5 player). Therefore, the win probabilities are interpreted as the probability of the hypothetical player beating the entire field. "Overall" is the average of our player quality measure for the entire field; "25 %" is the average for the highest 25% of players in the field; the other % terms are defined analogously
When using the "difficulty to win" measures to guage field strength, the PGA Championship emerges as the clear winner over this time period. It was the most difficult tournament to win for a Top 5 golfer in 5 of the 7 years in our sample (and was ranked second in the other two years); the story was similar for the average PGA TOUR professional.

Moving to measures of field strength based on average player quality, the story becomes more nuanced. Overall, THE PLAYERS has the highest average player quality in every year from 2011-2017; the Masters has the highest player quality when only considering the top 25% of players in a field (as well as 25-50%, and 50-75%). However, where THE PLAYERS is significantly stronger than any of the majors is in the bottom 25% of players in the field: it is more than a stroke better per round than the bottom quartile in any of the majors.

THE PLAYERS Championship should be considered the deepest field in golf. It is comparable to the major championships in terms of the quality of the top players in its field, and has substantially better players at the bottom end. However, it is not the hardest tournament to win. How do we reconcile these seemingly contradictory statements? The bottom quartile of golfers in these fields have only a very small chance of winning the event: even the (relatively) higher quality players that fill the final spots at THE PLAYERS do not make the event significantly more difficult to win for a Top 5 player. It is the players in these fields that rank between 30th and 60th that seem to make the difference (all have very similar players making up the top end of their field). The PGA Championship is slightly stronger than THE PLAYERS in this regard, making it the most difficult event to win in professional golf.