Multiple personality disorder: scientific and medicolegal issues.

Despite the intense study it has received since its inclusion in DSM-III, multiple personality disorder (MPD) largely remains an unvalidated construct. Definitional problems remain (there is not even agreement in the field as to whether a diagnosis of MPD truly means the existence of more than one personality), while the vagueness and liberality of existing criteria give the clinician little guidance in diagnosis. In forensic settings, diagnosis of MPD is even more problematic, since there is substantial evidence that the disorder cannot currently be phenomenologically distinguished from malingering. It also remains to be demonstrated that evaluators can determine whether alter personalities, if they exist, are truly unaware of each other, lack control over other alters' behavior, or are unable to know right from wrong.