## Background

The origin of this question is a conversation I had with some friends a few years ago. At the time, Roger Federer and Tiger Woods were dominating professional tennis and golf, respectively, and we were comparing and contrasting the two. It occurred to me that there was a mathematical question that was relevant to our discussion; namely, the structure of golf tournaments vs. tennis tournaments.

For example, the Masters is a four-round tournament. After two rounds, roughly the bottom half of the field is sent home. The winner is the person with the lowest total score after four rounds. On the other hand, Wimbledon is a single-elimination tournament; the winner must defeat seven other players in head-to-head competition. From a structural standpoint, if you are the best player in the field, is it harder to win a tournament like the Master's or harder to win a tournament like Wimbledon?

## The mathematics

More generally, how does a tournament's structure affect the likelihood that the best player will win?

This question is a bit fuzzy because there are some modeling issues involved that will affect the answer. Something like the following seems a reasonable place to start.

Let $F_1, F_2, \ldots F_n$ be independent normal distributions such that a random variable drawn from distribution $F_i$ gives the performance by the $i$th best player in a particular round of competition. So we would have $\mu_{F_i} > \mu_{F_j}$ when $i < j$. Assuming that the $F_i$'s have the same variance seems a reasonable starting point, too, as does the assumption that a given player's performances from round to round are independent.

First question: What is the best way to model the $\mu_{F_i}$'s vs. the $\sigma_{F_i}$'s? The difference $\mu_{F_1} - \mu_{F_2}$ ought to be much larger than $\mu_{F_{99}} - \mu_{F_{100}}$, so maybe something like $\mu_{F_i} = 1/i$ would work, but I'm not sure what makes for a reasonable variance to go with this function.

For specificity's sake, let's assume three types of tournament structure: 1) that of the Masters, 2) that of Wimbledon, and 3) that of the World Cup (which has a round-robin stage before moving to a single-elimination stage).

Second question: Given a satisfactory answer to the first question, what is the probability that Player 1 will win each of these three tournaments?

## My reasoning so far

It seems to me that the two most important factors involved that would prevent the best player from winning the tournament are

- an unusually poor performance from the best player in a particular round, and
- an unusually good performance from someone else in the field in a particular round.

There's not much that the tournament's structure could do to mitigate factor (1), although a single-elimination tournament would seem to be the most unforgiving. On the other hand, the structure of the tournament probably has a large effect on the impact of factor (2). For instance, an incredible performance from someone in two separate rounds of the Masters raises the bar quite a bit for the best player. On the other hand, in a tournament like Wimbledon two great performances might lead to two upsets of major players but doesn't provide any advantage in later rounds, and, for the best player to be negatively affected, he/she would have to be playing directly against the overperforming player. Also, if there are enough players around (like the early rounds of Wimbledon and all the way through the Masters) there is a high probability that someone in the field will turn in two great performances in two different rounds.

So, if you are the best player in the field it seems to me that contests in which you are essentially playing most of the field simultaneously, like the Masters, would be more difficult to win than single-elimination tournaments like Wimbledon, which in turn would be more difficult to win than those with a round-robin format in the early rounds and single-elimination in the later rounds, like the World Cup.

Third question: Are there any known results that address this problem of the effect of tournament structure on the best player's chances of winning?

I would be happy to see critiques/comments on my modeling and my reasoning as well.