Pooled variance
（重定向自Pooled standard deviation）
In statistics, pooled variance (also known as combined, composite, or overall variance) is a method for estimating variance of several different populations when the mean of each population may be different, but one may assume that the variance of each population is the same. If the populations are indexed ![i = 1,\ldots,k](/Images/godic/202502/03/57419b7c2597864a08a6bb014d96f34e2050.png")
, then the pooled variance ![s^2_p](/Images/godic/202502/03/39467b4d6f5542da275f0b52e42e979f2050.png")
can be estimated by the weighted average of the sample variances ![s^2_i](/Images/godic/202502/03/ab923d45cc02687c30b990701a2891b42050.png")