To the Editor: The article by Joan Ellason, M.A., and Colin A. Ross, M.D. (1), is remarkable for a profusion of highly significant findings that are not scientifically meaningful.

In follow-up, those who have fared worst will be dead, unavailable, or uncooperative. Ellason and Ross obtained follow-up information on only 40% of their cohort. The high degree of selection in their study radically undermines their findings. We get no idea how many patients have deteriorated to suicide or died of self-neglect, have become incarcerated or hospitalized elsewhere, are homeless or cannot afford a telephone, or have suffered other causes of unavailability. Such patients would be unlikely to raise scores for improvement.

Ellason and Ross make no reference to the natural course of untreated dissociative identity disorder. Without this information, it is unjustified to imply that improvement resulted from the treatment. The Dissociative Disorders Interview Schedule lacks even face validity. It may be able to give replicable findings, but reliability does not prove validity. Patients who act a part may act it the same way twice, but a part in a charade is not a diagnostic entity. Likewise, Ellason and Ross rely on the Dissociative Experiences Scale, but Hacking (2) concludes that scientists whose aim is to discover facts would be "thunderstruck" by the practices on which the scale is based.

Dissociative identity disorder is highly controversial (even on this continent), liable to be produced and maintained by suggestion, profoundly flawed in logic (3), and promoted by social role expectations (4). A controversial diagnosis requires particularly well-drawn criteria for evaluation. However, the use of Kluft"s (5) irredeemably nebulous "integration" criteria may trap the unwary. For example, Ellason and Ross accept "the absence of behaviorally evident separate identities." Yet Kluft has claimed that at the time of diagnosis, 40% of dissociative identity disorder patients may show no overt signs of the disorder (5). Perhaps Ellason and Ross excluded such cases from their cohort, but Ross himself (6) further complicates the matter. He warns that alter personalities may enter "inner hibernation," sometimes for lengthy periods in which state they do not manifest themselves to the outside observer. One wonders how the present authors determined that their subjects" improvements were not examples of this phenomenon.