Kuder-Richardson #21 Formula

[pkaraffa]

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

 

[FloMM2]

pkaraffa,
Let set some ground rules:
R is in Column H Row 1, k is in Column I Row 1, X is in Column J Row1, S is
in Column K Row 1.
Values to be entered into Row 2 of the above Columns, without "".
"=(I2/(I@-1)*(((1-(J2*(I2-J2))/(I2*K2)))))" in H2
"50" in I2
"43" in J2
"25" in K2
The answer I got was 0.774694.

hth
Dennis

 

[pkaraffa]

pkaraffa,
Let set some ground rules:
R is in Column H Row 1, k is in Column I Row 1, X is in Column J Row1, S is
in Column K Row 1.
Values to be entered into Row 2 of the above Columns, without "".
"=(I2/(I@-1)*(((1-(J2*(I2-J2))/(I2*K2)))))" in H2
"50" in I2
"43" in J2
"25" in K2
The answer I got was 0.774694.

hth
Dennis













- Show quoted text -

So did I. I just rounded up 0.774694 to 0.775 in which I rounded up
the 5 to make it 78 that's it.