what is the sign for population variance
The sample variance sÂ² is the best point estimate (or single value estimate) of the population variance ÏÂ². The sample standard deviation s is commonly used as a point estimate of Ï ( even though it is a biased estimator). (Sec 6-4 showed that sÂ² is an unbiased estimator of ÏÂ², but s is a biased estimator of Ï.)