The questionable validity of self-report measures in psychiatry has been the topic of a fewrecent posts here at Neuroskeptic.
Now an interesting new study looks at the question in issue from a new angle, asking: what kind of people report feeling more or less depressed? Korean researchers Kim and colleagues found that intelligence and personality variables were both linked to the tendency to self-rate depression more severely. The study involved 100 patients who'd previously suffered from an episode of depression or mania and who, according to their psychiatrist, had now recovered and were back to normal. Kim et al looked to see what the patient thought about their mood, by getting them to complete the Beck Depression Inventory (BDI) self-report questionnaire. This was compared to the clinican-administered HAMD scale (another Neuroskeptic favourite) which is meant to be independent of self report. It turns out that the BDI and HAMD scores were only weakly correlated - with a coefficient of just r=0.32. That's really not very good considering that, in theory, they both measure the same thing: 'depression'. Many people reported being considerably depressed when their clinicians rated them as fine. But more interestingly, certain characteristics of the patients were correlated with their self-report/clinician-rating discrepancy. Specifically, patients with a lower IQ, who were more impulsive, and less conscientious, tended to self-report more severe depression. Now, the uncharitable interpretation of these people is that they were just too sloppy to complete the form properly... the uncharitable interpretation of the psychiatrists is that it's their fault for underestimating depression in people less inclined to express themselves in 'the right way'. There's no way to know. Either way, it's a serious problem because it shows that self-report and observer-report measures of depression aren't just poorly correlated, they're actually measuring different things for different people. It could be even worse than it appears because the HAMD, although supposedly not a self-report measure, does in fact heavily rely on the patient's cooperation. So a 100% clinician-rated scale might be even further removed from self-report.
Kim EY, Hwang SS, Lee NY, Kim SH, Lee HJ, Kim YS, and Ahn YM (2012). Intelligence, temperament, and personality are related to over- or under-reporting of affective symptoms by patients with euthymic mood disorder. Journal of affective disorders PMID: 23270973