Perhaps, then, it is the case that depression is not a coherent, homogeneous psychological construct. It may instead be a hierarchical construct that involves shared variance among several, separable constructs (McGrath, 2005). Use of overall depression scores as a criterion in construct validity/theory testing studies is likely to be problematic. For example, to test whether stressful events are a risk factor for depression is imprecise: Are they a risk factor for each construct subsumed within the overall label? Are they a risk factor for only one construct, or for some subset of constructs? For example, do they tend to reduce positive affect but not influence negative affect? Or, do they increase negative affect but not relate to positive affect? Do they influence both? The imprecise test yields imprecise results. Following such a test, one does not have a coherent psychological finding.
