WTA Tennis Rankings Aren't Working

20 May 2017

In her first match at the Rome Masters, World No. 1 Kerber was ousted by the 68th ranked player on tour, Anett Kontaveit, in straight sets. Despite holding the best rank on tour, Kerber has seemed in a slump for most of the season with early round loses becoming a norm.

Kerber’s loss continues an undesirable streak for No. 1 seeds in the 2017 WTA season. Look across the 11 results at Premier-level events or better this year and you will not find a single No. 1 seed among their champions. Kerber’s loss in Rome this week brings that tally to 12.

This puts WTA No. 1 seeds on track to hit a startling low for title wins at top events. Since 2009, tour No. 1 seeds have won at least 15% or more of Premier and Grand Slam titles by the halfway mark of the calendar. 2016 was the first year that only one title was earned by the No. 1 seed by the end of the French Open. If Roland Garros crowns a lower seed this year, 2017 will be even worse with 0 titles won by No. 1 seeds.

But it isn’t just the No. 1s. If we look at the seedings of the champions and finalists for the 2017 season (see table below), we find that the disappointing results extend to all the top seeds. Among all champions at top events this year, only four have been won by one of the top 5 players in the draw, according to their seeds. At the same time, the same number of events have been won by players ranked outside the top 30.

So what’s going on? And who’s to blame?

Certainly not the players. The women’s tour has continued to deliver high-quality tennis and exciting storylines. Just consider the resurgence of Venus Williams, the collected consistency of Johanna Konta, or Eugene Bouchard’s impressive win over Maria Sharapova. Even with the absences of some of the biggest names (Williams, Azarenka, Kvitova, Sharapova) for all or part of the 2017 season, the tour is thriving.

Nevertheless, with the surprising results this year there are bound to be commentators who will say that WTA tennis players aren’t living up to their ranking. But I would argue that such commentators have it backwards. It’s the rankings that aren’t living up to the players.

One of the main purposes of the WTA Officials Rankings is for event seeding. Most tournaments use Official Rankings to not only decide who gets into an event but also how they should be placed in the draw, so that the best players are most likely to advance to the final rounds. The tournament is effectively making a prediction with each seed, the No. 1 their favorite for the title, the No. 2 the runner-up, and so on.

This means that, by and large, there is a direct relationship between a player’s ranking and expectations about their results at events. In fact, gurus of tennis statistics, Klaassen and Magnus, figured out a simple formula for converting a player’s ranking into the expected rounds they will reach at an event. Here is the formula:

As an example, if a player is entering a Grand Slam, the max round is 8 (total rounds + 1), and the expected round for the No. 1 seed is 8 (winning the title), for the No. 2 seed is 7 (being runner up), for the No. 4 seed is 6 (exiting in the semifinal), etc.

If rankings are doing their job well and draws are positioning the strongest players in the top spots, we should see good consistency between the rounds players are expected to reach and the actual rounds they reach. But, by this measure, the WTA rankings this year have been a disaster.

The figure below compares the actual and expected rounds for the champions and runners up at the 11 Premier and Majors that have been completed in 2017. The number on the y-axis shows how many more rounds a player reached than was predicted by her ranking. If the difference is negative, it means the player actually underperformed. You can see that for much of 2017, the winners and finalists at the top events have been out-performing their rank by 4 to 5 rounds!

The same breakdown for the same time period in 2016, shows that the failure of the rankings has been worse in 2017 but not by a huge amount. The inconsistency in 2016 was more in the range of 3 to 4 rounds, still a massive underestimate of player performance.

To get a sense of where we are and where we could be with rankings, consider what a perfect rankings system’s results would look like. The chart to the right shows that, when a rankings system was able to correctly pick the best and second best player at event, all differences between actual and expected rounds would lineup along the 0 line.

Asking for a “perfect” ranking system is perhaps unreasonable. But surely WTA players and WTA fans deserve a better ranking system.

How do we get there?

To start, the tour has to put a higher value on the performance of the ranking system and be open to change. If we can agree that a new system is needed and that performance is a top priority for the new ranking system, then the clear yardstick for judging alternative systems would be on the basis of how well they position players in tournament draws. This means looking for rankings with better predictive power.

I’ll take a look at what systems could offer such power in a future post.

Tournament	Start Date	Champion	Seed (Rank if Unseeded)	Runner Up	Seed (Rank if Unseeded)
Brisbane	2017-01-02	Karolína Plíšková	3	Alizé Cornet	41
Sydney	2017-01-09	Johanna Konta	6	Agnieszka Radwańska	2
Australian Open	2017-01-23	Serena Williams	2	Venus Williams	13
St. Petersburg	2017-01-30	Kristina Mladenovic	51	Yulia Putintseva	34
Qatar	2017-02-13	Karolína Plíšková	2	Caroline Wozniacki	18
Dubai	2017-02-20	Elina Svitolina	7	Caroline Wozniacki	10
Indian Wells	2017-03-13	Elena Vesnina	14	Svetlana Kuznetsova	18
Miami	2017-03-27	Johanna Konta	10	Caroline Wozniacki	12
Charleston	2017-04-03	Daria Kasatkina	42	Jeļena Ostapenko	19
Stuttgart	2017-04-24	Laura Siegemund	49	Kristina Mladenovic	17
Madrid	2017-05-08	Simona Halep	3	Kristina Mladenovic	14

If you liked this story, share it with your followers or follow this site @StatsOnTheT on Twitter.