Mental health articles

Dimensions of normal personality often shade into abnormality or at least social undesirability at one pole. However, only a few of these dimensions are explicitly conceptualized as vulnerabilities for psychopathology. These “diatheses” are particularly important constructs in the study of abnormal personality. If they are shown to be precursors of mental disorders, they may supply valuable etiological clues, may enable early detection of those at risk, and may serve as targets for preventive interventions. Personality diatheses are usually conceptualized as continuous dimensions that precipitate a mental disorder when a sufficient quantity of stress bears on the person. In short, both the vulnerability and the stress that triggers it are understood as quantitative factors, but the disorder itself is understood to be a discrete phenomenon produced by a kind of threshold effect. Each person has a unique threshold, set by his or her position on the vulnerability continuum; and if it is reached, then the clinical syndrome emerges.

Although this continuum view of personality diatheses is widespread, it is entirely plausible that diatheses could be taxonic. Only a discrete class of people might be vulnerable to a particular mental disorder, and no amount of stress could trigger the disorder in people who do not fall within the class. This model of personality vulnerability has importantly different clinical and research implications. It would imply that the assessment of vulnerability should involve assigning individuals to categories rather than distributing them along a quantitative scale. Psychological assessments might need to be calibrated to distinguish optimally between taxon members and nonmembers. The refi nement of such identifi cation procedures would have a major bearing on efforts at early detection and the prevention. Similarly, a categorical model would imply that a specifi c causal factor might underlie the vulnerability (e.g., a particular environmental condition, a major gene, or a particular neurochemical aberration), and that this causal factor might be an appropriate target for research. Understanding the latent structure of personality diatheses clearly has considerable importance.

To date, only a few potential personality diatheses have been investigated taxometrically. Most of this work is very recent, refl ecting an upswing of taxometric interest in vulnerability. The evidence that has emerged is interestingly discrepant for two diatheses, providing another rationale for further taxometric work. Clarifying the nature of vulnerability for major mental disorders should be a major focus of future research. Vulnerability to mood disorders has been examined in only three studies, a neglect that is surprising given the massive investment of research into vulnerability to unipolar depression. The fi rst study actually investigated vulnerability to bipolar disorder, examining the latent structure of hypomanic temperament (i.e., dispositional cheerfulness, energy, gregariousness, recklessness, and irritability). Meyer and Keller (2003) investigated this temperament in large samples of adolescents and young adults and found no evidence of a hypothesized taxon. Vulnerability for bipolar mood disorders would appear to fall on a continuum, pending further work. Two recent studies have addressed vulnerability to major depression, coinciding with a renewed interest among taxometric researchers in the latent structure of depression itself. Gibb, Alloy, Abramson, Beevers, and Miller (2004) conducted analyses of measures of depressogenic attributional style and dysfunctional attitudes in a very large sample of undergraduates, and obtained nontaxonic findings using three distinct taxometric procedures. However, Strong, Brown, Kahler, Lloyd-Richardson, and Niaura (2004) obtained a taxonic result in a study of treatment-seeking smokers assessed on a depression proneness inventory. The differences between the samples and measures employed in these studies may account for their discrepant conclusions, which indicate that further work on vulnerability to depression is urgently needed. Two additional vulnerability factors have received similarly limited taxometric attention. The structure of anxiety sensitivity, a diathesis for panic disorder that involves the fear of anxiety and anxiety-related sensations, has been examined in two published studies.Taylor, Rabian, and Fedoroff (1999) obtained a nontaxonic fi nding, whereas Schmidt, Kotov, Lerew, Joiner, and Ialongo (in press) found evidence of taxonicity. As with unipolar depression, then, there is mixed evidence on the structure of this diathesis. Vulnerability to dissociative disorders has arguably been examined by Oakman and Woody (1996), who obtained a taxonic fi nding for hypnotic susceptibility, a characteristic that is elevated among dissociators.

To summarize, personality vulnerabilities have received relatively scant taxometric scrutiny, with the exception of schizotypy. The evidence of the existing studies is intriguing. Whereas taxometric examinations of normal personality have rarely yielded taxonic fi ndings, such fi ndings have been common in studies of diatheses, directly challenging the default assumption that personality vulnerabilities are continua. More replication and extension to additional diatheses is required before this conclusion can be drawn with confi dence, but work conducted thus far clearly increases the plausibility of taxonic models of vulnerability. Most research on schizotypy supports a taxonic model, and some limited evidence of taxonicity has been obtained for vulnerabilities to panic disorder, dissociation, and depression. Continuing this work should be a priority.

Tags: diatheses, personality, personality diatheses