In examining content validity, they noted that most HAM-D versions contain core items that have remained unchanged for more than 40 years, while the DSM diagnostic criteria have been revised three times in response to developments in clinical trial research and expert consensus. Several symptoms in the HAM-D are not among the current DSM-IV criteria and several key DSM-IV depression features are "buried within more complex [HAM-D] items and sometimes are not captured at all."
There has been generally good convergent validity with other measures, although not with the major depression section of the Structure Clinical Interview for DSM-IV. This is further indication of the divergence of the HAM-D from current diagnostic criteria. In one evaluation of discriminant validity, four items (psychomotor agitation, gastrointestinal symptoms, loss of insight and weight loss) failed to differentiate depressed from healthy patients (Rehm and O'Hara, 1985).
Factorial validity was evaluated with factor analysis in 15 studies with 17 samples. There was not a single unifying structure replicated across studies, according to Bagby and colleagues. They noted that while the HAM-D is clearly not unidimensional, with separate sets of items reliably representing general depression and insomnia factors, "the exact structure of the Hamilton Depression Scale's multidimensionality remains unclear."
The HAM-D has shown predictive validity and been found more sensitive to change than the self-reporting Beck Depression Inventory (BDI) or Zung Self-Rating Depression Scale (ZSDS). Bagby and colleagues (2004) qualified the apparent predictive validity of the HAM-D, however.
"One disadvantage of a multidimensional instrument such as the Hamilton Depression Scale in detecting change is that specific treatments may affect only a single dimension," they stated. "If the total score includes somatic symptoms that actually reflect treatment side effects, estimates of treatment response will be spuriously low."
Calling for change, Bagby and colleagues contrasted the progress and sophisticated methods in developing new antidepressant medications with continued reliance on antiquated methods to assess change in depression severity and response to treatment.
"Effort in both areas is critical to the accessibility of new medications for patients with depression," the researchers concluded. "The field needs to move forward and embrace a new gold standard that incorporates modern psychometric methods and contemporary definitions of depression."
Kalali concurred with this assessment and is optimistic that the newly formed Depression Inventory Development Team will produce that instrument. "We are well aware of the need for a new depression rating scale based on our more recent understanding of depression and modern psychometric methodology," Kalali commented. "This effort is well underway with item development and field testing already in progress."