ใช้มาตรวัดเดียวกันกับคนกลุ่มเดียวกันในเวลาต่างกัน This is usually employed with dichotomous variables which are scored 0 for incorrect and one for correct.The Spearman-Brown prophecy formula is applied to the correlation to find out the reliability. Alternatively, the psych package offers a method of calculating Cronbach's alpha with a greater variety of arguments; see additional https://kr2005847.pages10.com/top-kr20-formula-secrets-62380655