Good morning.

I am tring to adapt the Kuder-Richardson #21 Formula to excel. I
appologize for linking the file to this post but I could not seem to
get the formts right for the formula. Basically the formula is used to
estimate test reliability. I can solve this long hand but would like
an excel formala to help me. Suppose we gave a 50 item test and the
mean was 43 and the variance was 25.0.

R =test reliability
k = number of items on the test
X = mean of the raw scores of the total test
S = the variance of the raw test scores from the total test


R = ( k ) (1- X(k - X))
---- -----------
k-1 kS

R = (50) (1- 43(50-43)
---- -----------
50-1 (50)(25)

R = (1.02) (1- 301)
-----
1250

Solve R:
R = (1.02) (0.76) = 0.78

Thank you in advance!
PJ

http://www.savefile.com/projects/808560688