Question: what is the difference between n and n-1 in calculating population variance?
Answer: The POPULATION VARIANCE σ2 is a PARAMETER of the population. ... Dividing by n does not give an “unbiased” estimate of the population standard deviation. Dividing by n−1 satisfies this property of being “unbiased”, but dividing by n does not. Therefore we prefer to divide by n-1 when calculating the sample variance.