You cannot use this variance for predicting a second engine match from a first match engine result, in that case you need to multiply it by 2.Adam Hair wrote:My actual source is a statistical textbook, but the Wikipedia entry for "prediction interval" also has the formula for computing the endpoints of the interval. For computing the variance, I used the approximation Error = 100%* Sqrt((score*(1-score)-0.25*draw%)/games).
See the "prediction interval" Wikepedia page you refer to, paragraph "Unknown mean, known variance".
http://en.wikipedia.org/wiki/Prediction_interval
The variance for predicting a future "observation" is (1 + 1/n) larger than the known population variance, with n the number of previous observations.
In this case we only have a single previous "observation" (engine match), so n = 1 and the variance is twice as high as the population variance.
This leads to 1.4 times higher error bars than the formula you cite above, exactly like I said in my previous post.
Robert