Before revision: If it is important to use unbiased operators then the sum of squares should be divided by degrees of freedom (n − 1) and the probabilities are multiplied by Kuder-Richardson Formula 21 (KR-21) Often discussed in tandem with KR-20, is Kuder-Richardson Formula 21 (KR-21).
After revision: If it is important to use unbiased operators then the sum of squares should be divided by degrees of freedom (n − 1) and the probabilities are multiplied by Kuder–Richardson Formula 21 (KR-21) Often discussed in tandem with KR-20, is Kuder–Richardson Formula 21 (KR-21).