To be frank, I was seeking to show that there was no validity to low levels of pathology and therefore the DSM-5 group probably is getting into dangerous territory. In fact, we found that there were rather significant and robust differences between individuals with 0 criteria and 1 criterion.7 Even though this finding didn’t support my hypothesis, I thought it was significant because it supported the DSM-5 Work Group and I felt compelled to publish that data.
We now had 2 interesting pieces of information. A few years ago we published a study on borderline personality disorder (BPD) that found once you hit the diagnostic threshold it made no difference how many criteria you met.8 On the other hand, when you were below the diagnostic threshold, having 1 criterion vs 0 made a big difference. In addition, a fair number of studies show that dimensional models capture more of the variance in personality pathology than categorical variables.9-12
This lead to our next study in which we hypothesized that dimensionality was only important when the person didn’t meet criteria, not when they did meet criteria.13 So we divided patients in the MIDAS study into those with 0 to 4 BPD criteria and those with ≥5 and counted the number of criteria that were met. Then we correlated each of those 2 dimensional scores with various indicators of illness severity, such as number of suicide attempts, number of psychiatric hospitalizations, and amount of time missed from work in the past 5 years. We found that for individuals who already achieved the diagnostic threshold there were very low correlations with these psychosocial morbidity variables. But for patients with subthreshold symptomatology, there were significant correlations and those correlations were significantly higher than the correlations for the other group. We therefore suggested that dimensionality is important but only when you don’t meet the diagnostic threshold. Thus, we came to the conclusion that DSM-IV already provides for capturing the important dimensional nature of PDs.
DR. BLACK: I’ve discussed this issue with a number of people who basically say doctors tend to think categorically, they don’t think along dimensions. Would it be difficult for psychiatrists to accept this type of system because it’s so different from how physicians are trained to think?
DR. ZIMMERMAN: I think doctors do think categorically and about traits, not necessarily disorders. For example, we’ll see a patient and a clinician will say he’s overly perfectionistic, but there’s no perfectionistic disorder in DSM-IV. This patient may or may not have obsessive-compulsive personality disorder.
I think assessment and diagnosis in routine clinical practice are not nearly as comprehensive as in research. I think psychiatrists often are picking up on traits that they think are clinically significant, but even within that context, they’re thinking categorically, that the patient is perfectionistic rather than rating him a 7 on a scale from 0 to 10 in terms of perfectionism.
Eliminated disorders
DR. BLACK: The proposal will cut the number of PDs to 6 plus personality disorder trait specified and those remaining are to be called types. How did the DSM-5 Work Group select the 5 (now 4) disorders to get rid of? Did they just pick ones that were infrequently used?
DR. ZIMMERMAN: They retained the disorders that were studied in the Collaborative Longitudinal Personality Disorders Study study14 plus others with well established validity.
DR. BLACK: What do you think about that plan to reduce the number of PDs?
DR. ZIMMERMAN: The biggest problem I have is that the DSM-5 Work Group didn’t present any data on the implications of their plan. The conceptual justification was to reduce comorbidity rates. Well, you can hypothesize that comorbidity would actually increase if you retained only those disorders that are more frequently comorbid with other disorders. Would there be any individuals who only have 1 of the excluded diagnoses? Would there be false negatives? They didn’t indicate whether comorbidity would drop and by how much. And they didn’t indicate if there would be a potential impact on missing cases.
We did such an analysis because we had the data set available from the MIDAS project.15 We wanted to know if you excluded the 5 diagnoses that (at the time) were proposed for exclusion—narcissistic, paranoid, schizoid, dependent, and histrionic—what percentage of individuals would no longer be diagnosed with a PD? Second, how much would comorbidity rates change? And third, how did individuals who would no longer be diagnosed with a PD compare with individuals who never had a PD?