It follows from these examples of heterogeneity that, for many disorders, the use of diagnostic status or a disorder score as either a predictor or a criterion in theory-testing studies will tend to produce unclear results. A score on depression, or a depression diagnosis, reflects scores on several constructs. To test a theory that Experience X is a risk factor for depression is to be imprecise. It may be the case that Experience X is a risk factor for one factor within depression but not for other factors. A proper test of that possibility requires assessment of the separate components of depression and examination of the association between Experience X and the target factor. If, instead, one used an overall depression score, one would risk missing the association altogether. If none of the other components of depression were related to Experience X, then the use of an overall depression score would essentially average the effect of the target factor with the irrelevant components, perhaps thus obscuring the importance of the target factor.
