An editorial article I saw at Cambridge Journals Online while scanning the freebies: Chronic fatigue syndrome and depression: conceptual and methodological ambiguities It talks about the relationship between CFS and depression in general (does one cause the other, result of illness, etc), but also has a section on the problems of using depression questionnaires which include symptoms that could be attributed to physical causes: Thus BPSers will assume any questionnaire is fine, because we have no physical disease, and in the process of using those questionnaires may incorrectly conclude that ME/CFS is psychological, because the questionnaire says so. This suggests that the assessment of depression among ME/CFS patient depends, to some extent, on the questionnaire being used. The author specifically recommends some scales: The Hospital Anxiety and Depression Scale: (this one isn't too bad, but ME patients will score a few points for physical and cognitive symptoms). The Profile of Mood States: from wikipedia: "The long form of the POMS consists of 65 adjectives that are rated by subjects on a 5-point scale. Six factors have been derived from this: tension-anxiety, depression-dejection, anger-hostility, fatigue-inertia, vigor-activity, confusion-bewilderment." The SCL-90: I have no idea why she likes this one. Looking at the questions it seems like almost 40 out of 90 questions could be attributed to physical causes, and only 12 of those are intended to be somatization questions. Also a lot of "Feeling nervous/afraid of situation involving physical/cognitive activity X". And she also specifically points out problems with the long version of the Beck Depression Inventory (very popular in CFS studies), which has a subsection for somatic complaints, and suggests omitting that section: Generally I think the author is on the right track, but has a limited understanding of ME/CFS, due to the case definitions she's looking at: for example, the Hospital and Anxiety and Depression Scale is probably a bigger problem than she seems to realize. As a result she congratulates Wessely for removing fatigue-based questions from one psychiatric questionnaire, but doesn't spot the same problem with relation to PEM, GI problems, sleep problems, pain, OI, cognitive dysfunction, etc. So applying her basic theory to CCC/ICC case definitions and cohorts could result in obtaining very different results regarding the prevalence of mood and other psychiatric disorders in ME patients, compared to modifying questionnaires based solely on CDC or Oxford criteria. The citations she lists above are for: Cavanaugh, S., Clark, D. & Gibbons, R. (1983). Diagnosing depression in the hospitalised medically ill using the Beck Depression Inventory. Psychosomalics 24, 809 815. Millon, C, Salvato, F., Blaney, N., Morgan, R., Mantero-Atienza, E., Klimas, N. & Fletcher, M. A. (1989). A psychological assessment of chronic fatigue syndrome/chronic Epstein-Barr virus patients. Psychology and Health 3, 131-141.