Suppose one believes a measure actually represents two dimensions and thus subsumes two constructs. Because determination of dimensionality is a theory testing process, there are at least two pieces of relevant empirical evidence. First, one is likely to conduct a structural test of dimensionality, such as factor analysis or latent class analysis, on theoretically appropriate samples. Second, to say that there are two dimensions is to imply that the two dimensions play different roles in psychological theory. If two putative dimensions do not play different roles in theory—that is, if, in every case, measures of the two dimensions correlate the same with measures of other constructs; predict the same external behaviors, attitudes, and cognitions; are equally heritable; and are related to the same gene polymorphisms—then there is no evidence that the two measures reflect meaningfully different psychological processes. The use of two terms and two measures would be both unnecessary and potentially misleading. The validity of the claim that the two are distinct has been compromised.
