One of the worst arguments to make during a GOAT debate is that a certain player belonged to a stronger era than another. It's an argument that is purely subjective, because there is no method of measuring how strong one era is compared to another. However, when comparing players from the same era, it is crucial to compare the quality of opponents that each player faces.
There are many ways to measure a player's strength of schedule and it has been measured by many people in many different ways. My contribution here should be seen as one more angle from which to view the topic.
What I want to do is compare the frequency with which Roger Federer, Novak Djokovic and Rafael Nadal have had to face the other ten best players of their era. So we will need a total of 11 players, and we already have three. Other wise people may have picked a slightly different group of 11 players, but these are the ones I selected to compare along with the Big Three: Andy Murray, Stan Wawrinka, Juan Martin del Potro, Marin Cilic, Kei Nishikori, Jo-Wilfried Tsonga, Tomas Berdych and David Ferrer.
Matches played against the group:
1. Djokovic - 284
2. Federer - 250
3. Nadal - 247
Regardless of who you support in this debate, we can all stop and admire the fact that each of these three have played about 250 matches against the same 10 players in their careers. Djokovic leads this comparison by 34 matches, which is even more impressive when considering that he has played the least professional matches of the trio.
Percentage of all professional matches in which the opponent is from the group:
1. Djokovic - 28.23%
2. Nadal - 22.31%
3. Federer - 17.37%
That is a staggering advantage for Djokovic and it begs the question: why such a big gap? I don't think Craig Tiley is behind this one. There are a few reasons for the difference.
Why Nadal's percentage is lower...
Nadal's best surface is clay, which is the surface on which few big events are held. As a result, Nadal puts more small events on his schedule where he is less likely to face the top players in the game. Ferrer also has a similar schedule which is why the Spaniards played each other 31 times, which is the third most Nadal has faced any opponent. Still, the kind of tournaments where Cilic is going to make a deep run are not the same tournaments that Nadal is winning, so he is less likely to play that kind of player as frequently. Nadal also suffers more early-round losses than the other two, because he is less successful on grass and hard courts.
Why Federer's percentage is lower...
Like most of the rest of the group, Federer is more likely to do well on hard and grass courts. However, Federer is also older than everyone else on the list. Had the list featured players like Andy Roddick, David Nalbandian or David Ferrer, Federer's percentage would be slightly higher. Federer's career has spanned almost two decades, so his numbers would always be slightly lower regardless.
Why Djokovic has the highest percentage...
Djokovic, more than any player in tennis history, is dominant on all three surfaces. In nearly every tournament that Djokovic has played in his career, he is reaching the stage where he is going up against the best players of his era. Even when Djokovic doesn't win tournaments, he frequently reaching the finals and semifinals of tournaments. That's why Djokovic has more weeks at No. 1 than Nadal despite having less Grand Slam trophies.
Anytime someone wants to compare the win-loss records of Djokovic, Federer and Nadal in a GOAT debate, they must also look at who the three players played against. The data makes it clear that Djokovic is consistently playing against better opponents than what Federer and Nadal are having to face.
