[winxordie]

"This better way of computing variance goes back to a 1962 paper by B. P. Welford and is presented in Donald Knuth's Art of Computer Programming, Vol 2, page 232, 3rd edition. Although this solution has been known for decades, not enough people know about it."

I'd generalize that to "although Knuth's book has been around for decades, not enough people have read it yet."