Originally Posted by mightyrick
That list isn't year end number one. It is the number of years that a player has reached number one at any point in the year.
Even if a player was only number one for five weeks, they still have to win enough tournament points to achieve that ranking. This ordinarily takes a player months to do. It actually is a very good metric across eras.
The point system has changed a few times over the decades. But across eras, to achieve number one, you always have to win the aggregate of the most important tournaments.
Are you sure about this list? If all you are referring to is being ranked number one at any time during a given year, than you are pretty far off for Federer. I have eight years total for him (2004-2010, 2012).
Fed's periods of being number one:
Feb. 2, 2004 - Aug. 17, 2008
July 6, 2009 - June 6, 2010
July 9, 2012 - Nov. 4, 2012