Mental disorders and burden of disease: how was disability estimated and is it valid?

OBJECTIVE: The Global Burden of Disease study found mental disorders to be the world's leading cause of disability. Few studies have examined the validity of the novel approach used to estimate disability, the person trade-off preference method. This paper describes, and examines the validity of, the burden of disease person trade-off protocol.
METHOD: The person trade-off provides preferences for health states (how good or bad you think it is in relation to perfect health). General practitioners (n = 20) with training in mental health provided preferences for 19 mental disorders using the person trade-off method. Descriptions for the mental disorders were derived from the average symptom severity and disability observed in the Australian National Survey of Mental Health and Wellbeing. Validity was investigated by comparison with two other methods (rating scale and rank order).
RESULTS: The general practitioners found the person trade-off complex and affronting. Only a moderate concordance was observed with two validity comparisons; however, validity was significantly increased following the opportunity for group discussion among the clinicians. The disability weights were higher than those used in the global study, a possible consequence of differences in disorder descriptions.
CONCLUSIONS: The present study is limited by small subject numbers and by using only one type of key informant (clinicians). While this study provided some evidence for the validity of the person trade-off, it also echoes concerns from recent commentaries about the feasibility of this method. These concerns are particularly relevant for mental disorder burden, which relies heavily on the magnitude of the disability weights. Further work is required to ensure that disability burden is validly estimated, and thus can appropriately be used to inform mental health policy.