http://spssx-discussion.165.s1.nabble.com/question-about-measure-creation-statistics-tp5002888p5005723.html
Cronbach's alpha serves as a reliability coefficient both for dichotomous
and scaled-score items (not, "polytomous" items).
I gather that both KR-20 and KR-21 are used for dichotomies, where
KR-21 is a simpler formula for hand calculation, usable under an
unlikely assumption. No one would use it these days, since no one
bothers with the tedium and inaccuracy of hand-calculations.
KR-20 matches one version of Cronbach's alpha.
"Polytomous" describes categorical items when there are more than
two categories. If they are "ordered" categories, I would always say
"ordered" or "scaled".
--
Rich Ulrich
Date: Fri, 18 Nov 2011 16:06:43 -0500
From:
[hidden email]Subject: Re: question about measure creation statistics
To:
[hidden email]
Sorry for the last post, I've mixed
20 and 21.
Anyway, Both are for dichotoimous items,
and KR-20 is mathematically equivalent to Cronbachs alpha
Michael, you said:
> First, that in fact, I should
be using KR-21 since the answers are not
> dichotomous.
If your answres are not dichotomous
you should not be using any KR reliability estimate.
Cronbacdh alpha is both for dichotomous
and polytomous scored items.
Andrés
[snip, previous]