It is important to appreciate that determination of homogeneity, like the determination of validity (Borsboom et al., 2004), must be based on theory and cannot be answered solely through statistics. Empirical evidence concerning dimensionality should be evaluated with respect to the theoretical appropriateness of the test. For example, one cannot view emergence of a single factor in factor analysis as necessarily indicative of unidimensionality. If one were to conduct a factor analysis on items representing a broad range of constructs, one whole domain may fall on a single factor and thus seem unidimensional. But a factor analysis on items restricted to that domain may identify subdomains within it, and that result suggests that the domain is multidimensional. The latter test may be a more appropriate test of one's theory of dimensionality.
