164 II. BIOLOGICAL  FOuNDATIONS
amentally high levels of N/NE are at in -
creased risk for developing a broad range 
of internalizing, externalizing, and “odd” 
or “peculiar” disorders, so the likelihood 
that they will develop more than one disor -
der is increased as well. Similarly, individu -
als’ temperamental level of DvC affects the 
probability of their developing one or more 
“externalizing” disorders, such as substance 
use disorders, ADHD, psychopathy/antiso -
ciality, and other forms of PP. Furthermore, 
this view facilitates the generation of hy -
potheses regarding other comorbidities both 
within and between clinical syndromes and 
PP, respectively. For example, if the comor -
bidity patterns of different types of eating 
disorders with other clinical syndromes and 
PP reflect common underlying temperament 
diatheses, the fact that patients with bulimia 
nervosa are higher in DvC than those with 
anorexia nervosa (Cassin & Von Ranson, 
2005) would lead to the prediction that buli -
mia patients have a higher rate of comorbid 
antisociality, which is, in fact, the case (San -
sone, Levitt, & Sasone, 2005).
In turn, this approach raises the ques -
tion of how best to conceptualize diagno -
ses. Clearly, it is untenable to argue that the 
DSM disorders represent distinct indepen -
dent entities in the way that chicken pox is 
independent of measles. Given what appears 
to be a universal penchant for categoriza -
tion, it is unlikely that the current diagnostic 
taxonomy will be replaced with a purely di -
mensional system in the immediate future. 
However, it is not improbable that tempera -
ment dimensions might provide the basis for 
a systematic reorganization of diagnoses, 
using the robust factors of internalizing, 
externalizing and oddity as the foundation 
for a new taxonomy. In fact, such a proposal 
was considered seriously by the Diagnostic 
and Statistical Manual of Mental Disorders 
(DSM-5; American Psychiatric Associa -
tion, 2013) Task Force but not implemented 
owing to concerns that the field is not ready 
for such a major “paradigm shift” either 
psychologically or empirically; that is, that 
more research is needed to provide a suffi -
ciently detailed dimensional taxonomy for 
actual clinical use.
Diagnostic severity is the second major 
challenge to categorical systems of diagnosis that is addressed by adopting a dimensional, 
temperament-  based approach. Under the 
current system, a certain threshold of sever -
ity must be passed for an individual to re -
ceive any given diagnosis. However, in many 
domains of psychopathology, subclinical 
cases have been shown not only to exist with 
high prevalence but, more importantly, to 
represent a serious public health problem in 
terms of personal suffering, increased psy -
chosocial dysfunction, and economic con -
sequences such as unemployment, increased 
sick days, and lower productivity (e.g., Judd 
et al., 2000). Thus, the distinction between 
above-  threshold and subclinical cases ap -
pears to represent an arbitrary rather than a 
true natural boundary between disorder and 
nondisorder. This observed lack of a distinc -
tive boundary is predicted from a dimen -
sional temperament perspective.
As we did with in the section on correlates 
of the Big Three, we take this opportunity 
to present findings from our own research 
to illustrate links between these dimensions 
and psychopathology. Table 6.6  presents 
correlations of N/NE, E/PE, and DvC, plus 
its subscales, with various forms of psycho -
pathology assessed both via self-  report and 
interview. The data are from the Improv -
ing the Measurement of Personality Project 
(IMPP). The sample, procedures, and mea -
sures are described in more detail in Clark 
et al. (2015, 2020), except that the sample 
size for these data is approximately 300 each 
(exact numbers vary due to small amounts 
of missing data) of (1) “high-risk” commu -
nity adults (HRCs), screened in for scoring 
above the cutoff point on the Iowa Personal -
ity Disorder Screen (Langbehn et al., 1999) 
and (2) 300 psychiatric outpatients. Mean 
age was 45.6 years ( SD = 13.4; range = 
18–84), 56.5% women, 78.1% White, with 
Black/African Americans as the largest mi -
nority group. The modal participant had 
some post-high school education (45.7%), 
with the modal HRC participant being mar -
ried or living with a partner (47.7%) and em -
ployed (43.7%), and the modal patient being 
single, never married (42.0%), and disabled 
(37.7%). Approximately one-  fourth of the 
HRC participants reported having received 
some kind of mental health treatment in the 
past.