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Subject: ELO isn't a normal bell curve, without some transformation

Author: Stephen A. Boak

Date: 20:30:56 06/04/02

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hi Dan,

1. Since Elo's system defines (by design choice!) each specific rating
difference in terms of a specific expected scoring percentage, regardless of
where the two ratings fall on the scale, I suspect (but am not sure, not having
worked out the math yet on paper) that the simple plotting of ratings in a
histogram would not be a normal bell-shaped curve.

Wouldn't some transformation be required to convert such ratings into
'normalized' figures which *theoretically* might look more like a bell shaped
curve?

2. Over time, as new & improved program versions & ratings rise, due to advances
in chess programming algorithms & techniques (and hardware improvements,
perhaps), wouldn't the overall plotting of ratings on a histogram (roughly from
older, weaker programs to newer, stronger programs) more closely follow the
growth curve for average rating of each new crop of released program/hardware,
rather than the normal bell curve.

3. Perhaps any program crop released within a relatively short span of time (say
a year or so) would have ratings plottable (with transformation, as noted above)
that closely approximate the normal (bell) curve.

Your thoughts on these ideas would be welcome.

--Steve






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