Dr. Ross and Ms. Ellason Reply

To the Editor: Our study has methodological limitations, as do all psychotherapy outcome studies in psychiatry. What limited conclusions would an unbiased observer be likely to draw from our data? It seems reasonable to conclude that certain extreme claims have been ruled out. For instance, patients receiving the diagnosis of dissociative identity disorder do not always deteriorate, and some do extremely well. For many patients, dissociative identity disorder therapy of the type we advocate (1) is correlated with remarkable reductions in a broad range of psychopathologies that do not seem to be accounted for plausibly by spontaneous remission.

Our study provides the most scientifically sound treatment outcome study to date for this group of patients. Drs. Merskey and Piper have provided no data of any kind demonstrating that the diagnoses and treatment they prefer for this population result in a superior outcome or in savings to the health care system. It is clear from their published words on the subject that they are ideologically opposed to our school of thought; however, the time has arrived for them to test their hypotheses rather than simply reiterate them. Our more detailed responses to Merskey, Piper, and Hacking are available elsewhere (1).

Without a reliable method of diagnosing dissociative identity disorder, no scientific discussion of differential treatment outcome is possible; therefore, the Merskey-Piper model can never be tested scientifically without the Dissociative Disorders Interview Schedule or an equivalent. Kluft has provided the only operationalized criteria for remission of dissociative identity disorder; without such criteria, there can never be a scientific demonstration that the Merskey-Piper method results in superior outcomes. If they have superior measures or any data to present, we would welcome them as worthwhile additions to the literature.

The scientific meaning of our study is not that it answers all questions for all time; rather, it establishes a methodological threshold that must now be met by competing schools of thought. Scientific debates about the validity of dissociative identity disorder and the best treatment for it have now moved beyond the anecdotal level. Criticism of studies is part of the method of science, but the criticisms must meet minimal intellectual and scientific standards.

Insisting that the Dissociative Disorders Interview Schedule does not have face validity contributes nothing to science. The Dissociative Disorders Interview Schedule incorporates the DSM-IV criteria for somatization disorder, major depressive disorder, borderline personality disorder, and the five dissociative disorders. To state that these sections of the Dissociative Disorders Interview Schedule do not have face validity is idiosyncratic, since all these diagnoses have been officially endorsed by APA. The DSM-IV criteria for dissociative identity disorder must have face validity with a large number of influential academic psychiatrists even to be in the DSM-IV. These psychiatrists could all be deluded, but that’s the way it is with face validity. Face validity does not establish any other kind of validity.