A newly published paper from Rhode Island Hospital argues against the proposed changes to redefine the number of personality disorders in the upcoming Diagnostic Statistical Manual, 5th edition (DSM-5). In their study, the researchers found the current scoring used in the DSM-IV already captures the dimensional nature of personality disorders. The paper is published in the Journal of Clinical Psychiatry and is now available online in advance of print.

The DSM-IV currently defines 10 different personality disorders. One of the proposed changes for DSM-5 would introduce a dimensional model to the categorical system, noted Mark Zimmerman, M.D., director of outpatient psychiatry at Rhode Island Hospital and lead author of the paper. Zimmerman and the researchers argue that there already exists a dimensional component in the current DSM-IV that can be used to identify some traits of a disorder even when the full criteria are not met. Thus, according to DSM-IV the personality disorders can be rated on a three-point dimensional scale with a rating of 0 indicating no traits for the disorders are found; 1 indicating sub-threshold traits; and a rating of 2 indicating the disorder is present.

Using this scoring method, Zimmerman and his group studied 2,150 psychiatric outpatients and evaluated them with semi-structured diagnostic interviews for DSM-IV defined disorders and measures of psychosocial morbidity.

Zimmerman says, "What we found is that the DSM-IV three-point dimensional approach is an effective method in identifying personal disorders and these findings raise questions as to whether or not there is a need to modify the DSM-IV for personality disorders at all. We propose, instead, that we call more attention to the fact that there is a quasi-dimensional approach already built into the existing DSM-IV."

In their study, the researchers found the three-point dimensional convention embodied in DSM-IV was more strongly associated with measures of psychosocial morbidity than categorical diagnosis, and that there was no difference between the three-point, a 5-point and a criterion count method of scoring the DSM-IV personality dimensions. This argues against changing DSM-IV to the dimensional approach proposed for DSM-5.