ใช้มาตรวัดเดียวกันกับคนกลุ่มเดียวกันในเวลาต่างกัน A Be aware within the equivalence of KR20 and Cronbach’s alpha for dichotomous knowledge: These will often be stated for being just equal; even so, algebraic equivalence only happens once the biased estimator of the sample variance which divides by the number of subjects n is useful for Var(Xi) https://kuder-richardson-formula25927.tinyblogging.com/a-simple-key-for-kuder-richardson-unveiled-70365584