There isn't any direct process choice for calculating the KR21, that is determined by the (ordinarily unrealistic) assumption that every one items in the size have equivalent difficulty levels (i.e. equal proportions of 'successes' around the products). The KR21 can be calculated in SPSS by using the AGGREGATE We suggest https://what-is-kr-2029360.pointblog.net/the-kuder-richardson-reliability-diaries-67688350