Mongrel wrote:

Doesn't a z-score calculate the number of SD's away from the mean?

I'm into it, should be easy to calculate.

Yes. That's it. Easy? For one type of rolling, yes. For mixed types? Can't wait to see what you have in mind :)

I found this post on talk-stats.com with a similar problem, and the answer was:

If you have the means and standard deviations that correspond to each z-score, you can:

(1) compute the overall mean and then
(2) get a good estimate of the overall standard deviation by adding up the individual variances, dividing by the number of sets and then taking the square root

Anyone with more math knowledge than me want to comment on the correctness of that solution?