• Use sumprod() which is faster, simpler, and more accurate than rounding each multiplication before summation.
• For an additional speed-up and simplification, compute the (x_xi - bar) only once instead of multiple times.
• For Spearman's rank correlation, we can skip the (x_xi - bar) step because the ranks are centered around zero.

Linked PRs

• GH-102670: Use sumprod() to simplify, speed up, and improve accuracy of statistics functions #102649