One of the major tennis storylines of 2017 has been the opening up of the field on the WTA tour.
With a number of former dominant players, like Serena Williams and Victoria Azarenka, out of the game and others, like Maria Sharapova and Petra Kvitova, still early in their return, 2017 has presented a massive opportunity to the tour’s ‘rising stars. Out of 13 Premier and Grand Slam events completed this season, 10 different women have taken the title win. This has given tennis fans many possible picks for who will emerge as the next major threat on the WTA tour.
The carousel of champions we have seen in the first half of the 2017 WTA season has made many ask whether this is one of the wildest period in WTA history?
When we experience a period in which match results are fundamentally less predictable, we can expect this to have been caused by an increase in depth and decrease in consistency. In other words, the difference in ability between any two top players is minuscule and more players have a chance for a title run on any given week.
Because Elo ratings update with every match result, it is a useful metric for measuring the depth and consistency of the tour over time. The chart below measure depth from 1990 to the present, focusing on the top 30 players at any point in time (e.g. roughly equivalent to the number of seeds at a Grand Slam).
Here depth in any given month is based on the difference in Elo rating between the player with the highest rating and the the player with 30th highest. The more narrow this difference the greater the depth. The smooth ups and downs in depth denote clear epochs of the tour. During the mid-1990s when Steffi Graf dominated the tour and was nearly untouchable, depth was at a low. Another period of low depth emerged in 2001 and 2002 when Venus Williams, Lindsay Davenport and Serena Williams had a string of strong results.
In general, we see the gap closing over time indicating a general trend toward greater depth since the early 2000s. The current period shows a new turn toward greater depth after a period from 2011 to 2014 when the gap in ratings was widening owing to the force that is Serena Williams.
In terms of consistency, I’ve looked at the average change in each top 30 player over the next 6 months. A large positive change tells us that top players were generally improving and winning more matches at that period, while a large negative changes suggests that the top players were on the decline.
The very last point refers to the start of the 2017 season and it shows that, over the next 6 months, the top players at the start have generally under performed with the average change in Elo ratings being a loss of 20 points.
All together, these two dimensions of tour performance show us that 2017 has been a period of some of the greatest depth the tour has seen in 30 years with more new faces contending for a spot at the top. These are all of the characteristics we might expect when the tour is undergoing a changing of the guard.
What previous epoch was most like the one we appear to be experiencing in 2017?
Since 1990, the pattern we appear to be headed for is most like the start of 2003, which followed several years of low depth, when Venus Williams and Davenport were racking up titles and Serena Williams had one phenomenal season in 2002. As those players went through a period of decline, Kim Clijsters and Justine Henin leapt to the top of the rankings and captivated the sport for several years.
If the next phase for the WTA brings us a similar rivalry and depth of talent, there is much to look forward to.