In every tournament, players are seeded into the draw to avoid
that they eliminate each other in early rounds. Because the tournament
directors want the best players to be there for a long time they seed them
in such a way that the #1 seed may not play against the #2 seed until the
final. Also, #1 or #2 may not play against the #3 or #4 until the semifinal,
and so on. The seed pairs (1,2), (3,4), (5,6) and (7,8) should each be
favored equally because the fact which seed of a pair goes into which half
of tournament draw is determined randomly. In most tournaments the seed
numbers are strictly determined by the current rankings of the players.
The better their ranking, the better their seed number.
Now I was interested in how the different seeds performed in tournaments since 1991. The chart below shows how often each seed won a tournament (dark blue) and how often each seed lost in a tournament final.
One can see that the #1 seed is more likely to win the tournament than
any other seed or unseeded players.
You can also see clearly that the number of tournament titles decreases with increasing seed number. When you take a closer look there is a slightly better performance of #4 over #3 and of #6 over #5. Of course there are more unseeded players among the tournament winners than any other seed except #1 because there are a lot more unseeded players than seeded players so their chance is much higher. The more interesting it is that #1 seeds win more tournaments than unseeded players.
The runner-ups perform the other way round - there are more runner-ups among the seeds #1, #3, #5 and #7 than among #2, #4, #6 and #8. There are more unseeded players who lose a final than who win a final.