STATISTIK-FORUM.de

Cronbach's alpha is widely believed to indirectly indicate the degree to which a set of items measures a single unidimensional latent construct. It is easy to show, however, that tests with the same test length and variance, but different underlying factorial structures can result in the same values of Cronbach's alpha. Indeed, several investigators have shown that alpha can take on quite high values even when the set of items measures several unrelated latent constructs.

The process of constructing homogeneous tests by examining itemtotal-score correlations and the value of coefficient alpha computed for the composite test score is not a fool-proof method. Both high item-total-score correlations and high coefficient alpha can be obtained in situations involving heterogeneous items. Perhaps the test constructor would be better advised to look both at the raw correlations among his items and perform a factor analysis of these correlations to see how tenable the notion of homogeneity is for his items.