David Richerby wrote:
JohnnyT wrote:
[...] you need to remember in ELO that the difference between 2500
and 2800 is vast, and the difference between 2800 and ~ 3100 is as
vast. It is not 10% better, it is closer to think of it as TWICE as
good. Or more likely to win MOST of the time. It is a HUGE
difference.

Specifically, an Elo-rating gap of 300 points (and it's the difference
that's significant so, yes, 2800 vs 3100 gives the same results as
2500 vs 2800, gives the same results as 1100-1400) corresponds to the
stronger player being expected to score roughly 85%. The approximate
values are tabulated below, by approximating the real data on FIDE's
website[1].

Rating diff. Score
----------------------
600 99%
500 96%
400 92%
300 85%
250 81%
200 76%
150 70%
100 64%
75 60%
50 57%
25 54%


Dave.

[1] http://www.fide.com/official/handbook.asp?level=B0210
Beware that the table is rather hard to read as the columns are
too narrow. The expected score is to the left of the rating
difference in each case.


Thank you, a complete explanation like this would be a good FAQ item.
(Is there a FAQ?)

I think this is important when looking at things like the computer
rankings so you can understand how measurably stronger than the field
Rybka is. And how far behind Crafty is is.

It is substantial, and gives tremendous credence to the argument that
the engine is substantially too weak to answer these questions in the
survey. Even if the questions are worth asking.

And I was just trying to add some anecdotal evidence that Fritz and
Rybka are often a 100cp apart in positions, and that value is not a
significant enough measure to say that Crafty is suitable. And that
indeed is even more weight that Crafty is unsuitable.