http://spssx-discussion.165.s1.nabble.com/Appropriate-to-use-Cronbach-Alpha-on-a-Yes-No-scale-tp4961283p4961924.html
I will expand on Tony's comment -
One version of alpha is computed directly as a function of
average r and K (number of items), and nothing else. (That
one assumes that variances are equal, which is not always assumed.)
- To reach a given alpha, you need 3 or 4 or more times the number
of items when items are dichotomies, not short scales.
- You certainly want to assure that your items are all scored
"in the same direction" in terms of the scale's latent dimension
since the program makes that assumption.
And I can expand on a comment in another post: every measure
of reliability (alpha, ICC, r, whatever) reflects on both the quality of
the scale and the variation existing in the sample. A sample with
lower variation on the latent dimension will always yield a smaller
measure for its reliability, other sources of error being equal.
--
Rich Ulrich
Date: Thu, 3 Nov 2011 11:33:46 -0500
From:
[hidden email]Subject: Re: Appropriate to use Cronbach Alpha on a Yes/No scale
To:
[hidden email]
How many items are you summing? The value of coefficient
alpha is related to the average item covariance/correlation and
the number of items. Also, make sure the covariance/correlations
are in the same direction.
From: SPSSX(r) Discussion [mailto:[hidden email]] On Behalf Of Mark Webb
Sent: Thursday, November 03, 2011 9:52 AM
To: [hidden email]
Subject: Appropriate to use Cronbach Alpha on a Yes/No scale
I'm attempting this and getting very low Alphas.
Is it advisable to use the measure with a 2 point scale?