
Chess rating system provides the best predictor of World Cup success - datageek
http://kaggle.com/blog/2010/06/14/quants-pick-elo-ratings-as-the-best-predictor-of-world-cup-success/
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leelin

      Are today’s crop better players? 
      Or like the economy, are Elo ratings subject to bouts of inflation?
    

Players leaving the system is one of the major sources of rating inflation in
chess. Even when rating changes of any single game is zero-sum, if a player
stops playing chess after a career of net losses, all the remaining players in
the world have more rating to divide up amongst themselves.

This is very obvious on FICS bughouse where new sock puppet accounts crop up
all the time, net lose several games, and then leave forever.

Part of the problem is new players are usually given a starting rating around
1600 (depends on their provisional games), a "median" ranking of sorts, but in
reality a new player is often far worse and donates rating as they slide down
to their correct rating.

~~~
carbocation
The last issue that you raised (new players donating ranking) has long made
sense to me. However, I had not considered inflationary pressure due to
players _leaving_ before. Is the inflation really from their departure, or is
it purely explained by their entrance, and loss of points while still playing?

~~~
s3b
Players leaving is a problem only if they lose points and then leave without
winning them back.

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paulnelligan
This looks like complete arse to me. 30 international games can span a 5-6
year period, during which time a completely new crop of players can emerge.
Where does form come into the equation?, England's performance the other night
was dismal, while Germany looked like potential winners. I've no clue how
Mexico made the top eight, perhaps because they're based in Central America,
and the competition isn't that stiff? And winners of the previous world cup,
Italy, in behind them at number 8??? ... get real!!

~~~
datageek
Good point on the 30 international games.

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carbocation
Sweet. I love Elo points a lot (so much so that they are how my startup ranks
U.S. colleges: <http://college.mychances.net/college-rankings.php> ).

The author poses the following question: "[...] like the economy, are Elo
ratings subject to bouts of inflation?" Since the amount of points available
depends on the number of individuals participating, Elo points should indeed
be subject to inflation.

~~~
grasshoper
Cool site. I knew Harvard's yield was higher than the other schools, but I
didn't expect Stanford and Yale to have higher yields so much higher than
Princeton. I don't think this was true a few years ago when I was applying to
schools.

How are you gathering information about where students were accepted? And
where is Caltech in all this?

Also, you know that you can't just add the 25th/75th percentiles for
individual SAT sections and come up with overall results, right?

~~~
carbocation
Thanks. Re: Caltech - if I recall correctly, there wasn't enough data for it
to produce results when I ran the algorithm last year. I suspect we'll have
enough this year (I'll probably re-run the algorithm in a few weeks).

Basically the entire site is dedicated to gathering information from students,
and then transforming that data into something useful for them. So I gather
the info directly (over 250,000 college apps from 50,000 different people are
in the system by now).

I honestly have no idea why I thought I could get away with adding together
the 25th and 75th percentiles for SAT subscores on that page; it's not
something I do elsewhere on the site. (I'm using "I" here since I'm sure this
is my fault alone.) Thanks for pointing that out!

Edit: I forgot about Princeton. The Elo points can be a bit hard to decipher
on the fly; for example, Yale should only beat Princeton in 59:41 fashion -
not exactly a drubbing. Here's an Ivy+Stanford+MIT cross-admit comparison
based on this data - [http://college.mychances.net/tools/college-choice-
matrix.php...](http://college.mychances.net/tools/college-choice-
matrix.php?list\[\]=342&list\[\]=544&list\[\]=3&list\[\]=1737&list\[\]=1519&list\[\]=165&list\[\]=1034&list\[\]=319&list\[\]=762&list\[\]=361)

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CWuestefeld
Table tennis uses a similar system. My wife used to play competitively, and
people at the club would always ask each others' ratings when looking for a
good match.

Of course, a single number can only tell you so much -- it's a very gross
generalization of skill. A lower-score player can have a particular strength
corresponding to another's weakness, thus leading to a win for the (generally)
weaker player. I imagine that this is similarly true for soccer teams.

~~~
lotharbot
> _"Of course, a single number can only tell you so much -- it's a very gross
> generalization of skill."_

In a system where new players can enter after competition has begun (and
others have accumulated points), there's also a good chance that a new player
will not yet have had enough time to accumulate a score that's in line with
their actual skill, which can lead to some misleading matchups. Depending on
the details of the ranking system and the ease of finding similarly-ranked
partners, it can take a long time to converge to a "true" rating.

For example: I had friends in college who played competitive card games that
had some sort of lifetime ranking (Bridge, perhaps?) Because they were young,
they were often the lowest seed in tournaments. Despite above-average skill,
they were normally eliminated by the very most skilled teams in the first
round, and therefore had few opportunities to accumulate points against more
equal competition. Once they finally broke through and won a couple of
tournaments, there was a bit of a snowball effect as they moved out of the
lowest seed.

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lazyant
A difference of two points in Elo is nothing; basically this corroborates the
current betting odds that Brazil & Spain are the two favorites with small
differences between them.

In any case football/soccer results have such a big variance that it doesn't
really matter. I think in HK there was a paper no long ago that studied soccer
competitions and sayed something like the best team in a soccer competition
only wins it a 30% of the time.

~~~
alex_stoddard
A big variance is going to occur in any direct elimination competition (which
the world cup is after the group stage).

(This has always bugged me regarding the baseball playoff system. It is a big
boost for teams economically but for purity I would prefer to see just a NL
and an AL league table).

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defen
So is there a way to compute the probability of one team beating another,
given their Elo scores?

~~~
carbocation
It depends on their exact formula. Roughly, though:

Probabilty of Team A beating Team B, given that Team A has 'A' Elo points and
Team B has 'B' Elo points: 100/(1+10^((A-B)/400))

