n vs n-1

People keep on wondering “Why is the denominator in the sample mean n, but the denominator for the sample variance is n−1?” All of us have had to answer this question at some time in our careers, either for our students or for ourselves. How do you answer it, and how helpful is your answer? Do you feel obliged to introduce distinctions such as populations vs samples, description vs inference, parameters vs statistics, Greek vs Roman letters? Or more advanced concepts, such as degrees of freedom, dimensions of subspaces, unbiasedness or maximum likelihood? Read more at:

http://bulletin.imstat.org/2012/12/terences-stuff-n-vs-n-1/