Question: Explain why the sample variance and population variance are computed differently.

• The numerators for the sample variance and population variance do not differ. SS is the numerator in both formulas; only the denominators differ for two reasons. First, the sample variance is unbiased when we divide SS by (n - 1)-on average, the variance of the sample will equal the variance of the population from which the sample was selected. Second, all scores in a sample are free to vary except one when the mean is known. So we divide the SS by one less than the sample size, called the degrees of freedom (df) for sample variance.