Zimmerman says, "In our previous report from the RI MIDAS project, we developed a briefer list of the symptom criteria of MDD that was composed entirely of the DSM-IV mood and cognitive symptoms. That simplified definition did not include the somatic symptoms." He continues, "Our initial research found high levels of agreement in diagnosing MDD between the simplified and DSM-IV definitions of MDD. Our goal in this study was to replicate these findings in a large sample of psychiatric outpatients, and to extend the findings to other patient populations, including those presenting for treatment of pathological gambling and candidates for bariatric surgery."

Zimmerman says, "After eliminating the four somatic criteria from the DSM-IV definition of MDD, leaving the five mood and cognitive features, a high level of concordance was found between this simpler definition of MDD with the original classification in all three patient samples studied." He adds, "This new definition offers two advantages over the DSM-IV definition ?? it is briefer and therefore more likely to be recalled and correctly applied in clinical practice, and it is free of somatic symptoms, thereby making it easier to apply with medically ill patients."

Using the Structured Clinical Interview for DSM-IV (SCID), the researchers conducted a study of more than 2,500 patients. The patient population consisted of 1,100 psychiatric outpatients, 210 pathological gamblers who presented for treatment and 1,200 candidates for bariatric surgery. Across all patients, the level of agreement between the simplified definition and the DSM-IV definition was more than 95 percent.

The researchers note that there are implications to changing the criteria for MDD. Because their findings indicate that the simpler definition is highly concordant with the current version, there would be no meaningful impact on prevalence rates. Reducing the number of criteria, however, would reduce the time needed to fully assess criteria in patients and diagnostic interviews could be shortened.

Zimmerman and the researchers conclude, "In deciding how to proceed in the next version of the DSM, the conceptual and practical advantages of a briefer set of criteria that is easy to apply to all patients, particularly medically ill patients, needs to be weighted against the disadvantages of deviation from tradition."