While calculating Guttman reliability by SPSS we find six values of reliability. Which one should considered appropriate and why?
Arun, Guttman proposed 6 measures as lower bound estimates for reliability based on different assumptions. Lamda 3 is equal to Cronbachs alpha. This index is based on quite restrictive assumptions, such as tau-eqivalence which means that all covariances between the items should be equal. This assumption is not necessary for Lambda 2. Therefore Lambda 2 is on most cases more appropriate than Lambda 3. Unfortunately,
... unfortunately, most researchers use Cronbach's alpha, but the assumptions are not tested. The other Lambdas are nowadays not used.
Karin
Lambda2 (Guttman, 1945) is a lower bound to the true reliability and equals the true reliability if the components are tau equivalent. Lambda2 is interesting because it always gives a lower bound that is as good as coefficient alpha but in some circumstances
may be considerably better.
Guttman is better since cronsbachs alpha has restrictive assumptions that are 90% of the time violated.
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