# bessel's correction

1. ### Modified population variance

I don't understand the term "modified population variance" used in this pdf file:///C:/Users/marya/AppData/Local/Packages/Microsoft.MicrosoftEdge_8wekyb3d8bbwe/TempState/Downloads/RSbook_ch3%20(1).pdf. Is it related to the concept of unbiased estimator of the population variance? Also, why do...
2. ### Why is the mean of sample variances not equal to the population variance?

Several texts say that the mean of all values of an unbiased estimator is equal to the parameter it is estimating. They also say that the sample variance using Bessel's correction is an unbiased estimator of the population variance. Here's what I'm confused about: Consider a population...