In an ANOVA the term Sum of Squares refers to an interim quantity used
in the calculation of an estimate of the population variance.
In a one-way ANOVA the Within Sum of Squares is a quantity used in the
calculation of the Within Mean Square. More specifically the Within Sum
of Squares divided by its Degrees of Freedom is equal to the Within Mean
Square. Under the Null Hypothesis, the Within Mean Square is an unbiased
estimate of the population variance.
Similarly, the Between Sum of Squares is a quantity used in the calculation
of the Between Mean Square. More specifically the Between Mean Square
is equal to the Between Sum of Squares divided by its Degrees of Freedom.
Under the Null Hypothesis, the Between Mean Square is also an unbiased
estimate of the population variance.
