- The most obvious one is bias towards your particular hero; I’m unlikely to convince anybody that I’m able to overcome this bias.
- There seems to be a generational bias, particularly in tennis. A currently dominant player is often labeled the greatest, especially by his/her peers.
- The opposite is sometimes true, I doubt some people will ever be able to admit that someone is greater than Pele (I think this is a particular problem in the arts with people like Shakespeare or Beethoven).
- Sportsmen are paid MUCH better now than they were 40 years ago and the pool of talent is MUCH bigger. This means it’s likely that super talents are both more likely to exist now and more likely to be recruited into a particular sport.
- It’s more difficult to truly innovate AND be effective now because almost everything would have been tried as a result of the above factors.
- Rivalries can distort thinking about greatness. Say Federer was a WORSE player and lost half of the finals he played in. Players like Roddick and Hewitt would be considered potential greats and worthy rivals. Some people would think of Federer more highly as a result of this change which would be ridiculous.
- Comparisons between today’s top players and past greats will always be difficult because relative incentive structure has changed so drastically.
What have I left out?
I think the best way of comparing top players from different eras would be to read all the match reports written at the time each player was active. Even then it would be important to take into consideration development in the style of sports writing; I’d guess that there is a trend towards reports being more worshipful these days.
Bottom line: In the absence of exceptional cases like Donald Bradman perhaps, it is pretty much impossible to sort these biases out.