An examination of neuroticism (N) and its ubiquitous association with most (if not all) forms of mental distress leads one to question whether item overlap of neuroticism with measures of anxiety and depression has artificially inflated estimates of these associations (see Ormel, Rosmalen & Farmer, 2004
). Though addressing this problem might seem relatively straightforward via the deletion of potentially overlapping items, Nicholls, Licht, and Pearl (1982)
criticized this approach and argued that the issue of item overlap actually presents a thorny dilemma to researchers. On the one hand, correlations between these measures might be artificially inflated due to overlapping items. On the other hand, Nicholls et al. argued that removing items potentially decreases the construct validity of the N measure. That is, if the potentially overlapping items tap what is theorized to be a facet of the construct, removing these items from one of the measures makes that measure less useful for examining the correlation between the two constructs.
In addition to the potential item overlap of N, Claridge and Davis (2001)
raise a second problem in using N to predict emotional disorders concerning the non-specific nature of the association between N and emotional disorders. That is, though elevations on N allow us to predict an increased risk of developing an emotional disorder, they don't allow for predictions of the specific form of disorder an individual is likely to develop. Claridge and Davis advocate for the identification of “the various expressions of N” that “have variance unique to themselves” - that is, particular facets of N, that have more specific power in predicting disorders, As an example of a disorder-specific risk factor, Claridge and Davis offer schizotypy as a predictor of schizophrenia. Schizotypy likely overlaps with N but provides a more specific predictive pathway between vulnerability and disorder. Following the logic of Claridge and Davis, deleting N items that potentially overlap with the emotional disorder being predicted might not only create the problems discussed by Nicholls et al. (1982)
but might also hamper the important search for disorder specific predictors.
The current study tests the extent to which item overlap accounts for the associations of N with both depression and anxiety. This study does so without removing overlapping items from measures and thereby also permits tests of likely disorder specific predictors. We begin with a brief overview of neuroticism, followed by a review of past findings concerning the associations of neuroticism with depressive and anxiety disorders (referred to collectively below as the emotional disorders). Next, we present the argument that neuroticism has item overlap with measures of emotional disorders. Finally, we present the results from a structural equation modeling approach to addressing item overlap without removing overlapping items that also provides a statistical basis for testing likely disorder specific predictors and for identifying facets of broad personality traits.
N has been defined as a relatively enduring palette of characteristics associated with a proclivity for experiencing negative mood states and sensitivity to stress (e.g., Eysenck, 1970
; Costa & McCrae, 1987
). According to Costa and McCrae (1992)
, N can also be broken down into six lower-order facets (anxiety, depression, anger, self-consciousness, vulnerability, immoderation/impulsivity). Though different measures of N vary with respect to the number and nature of the facets, there is nearly universal agreement that N encompasses the propensity to experience anxiety and depression (e.g., Eysenck & Eysenck, 1975
; Goldberg, 1981
; Goldberg, 1999
). Not surprisingly, N has been shown to predict increased risk for the development of depressive disorders. For example, longitudinal studies have demonstrated that N predicts the overlap. That is, Ormel and colleagues noted that the content of some N items was very similar to items on measures of depression and anxiety (or emotional distress), but was lacking specific qualifiers of frequency, intensity, and duration. They argued that N is merely a measure of an individual's typical degree of distress, and therefore, the association of N with emotional distress may simply tell us that individuals who report feeling depressed and anxious will continue to report feeling depressed and anxious in the future (also see Claridge & Davis, 2001
If there is significant item overlap between N and the emotional disorders that N putatively predicts, then predicting the disorders from their potentially tautological items might demonstrate little more than the stability of those items (Nicholls, Licht, & Pearl, 1982
). This overlap is especially salient for specific facets of N that are named for the disorder with which they putatively overlap (e.g., depression and anxiety facets). For the present study, content analysis of the depression and anxiety facets involved a qualitative, semantic comparison of N items to DSM-IV criteria for the relevant disorder. For example, particular items that load on the depression facet of N (such as “dislike myself” and “have a low opinion of myself”) could be interpreted as paraphrases of the “feelings of worthlessness” criterion for a major depressive episode or the “low self-esteem” criterion for dysthymic disorder. Similarly, items from the anxiety facet of N (such as “worry about things” and “fear for the worst”) are similar to the “excessive worry” symptom of generalized anxiety disorder (for further examples, see ). It is important to note that the problem highlighted by Nicholls et al. (1982)
did not define item overlap as precise agreement of the items between two measures. Specifically, Nicholls et al. clarified that the N items and DSM-IV symptom criteria in question need not be worded exactly the same; as long as some qualitative overlap is perceived, then the argument that item overlap may be artificially inflating correlations has viability (Nicholls et al., 1982
). Given that several items for the depression and anxiety facets on this and other N scales appear to be synonyms for symptoms of their associated disorders, the idea that there is content overlap between these variables is supported by our content analysis.
Examples of putative content overlap between the depression facet and anxiety facet of neuroticism with depressive and anxiety symptomatology
The present study will address both the problem of N nonspecifity as well as that of item overlap between N facets and their associated pathologies, by examining the specific predictive power of facets of N in comparison to that of the general N factor. That is, implementing a novel statistical approach as an alternative to deleting potentially overlapping items, the present analyses will compare a series of structural equation models (SEMs) that include both potentially overlapping facets of N (POFs) and non-overlapping facets of N (NOFs), a general N factor (GNF), and the emotional disorders. N is represented hierarchically in these models with the GNF representing the variance of N that is common to all items. These hierarchical models will be used to estimate the contribution of a POF (either the depression or anxiety facet, depending on the analysis) in comparison with both the NOFs and the GNF, without the methodological problems associated with deleting items. If the POFs of N do entirely or even largely account for N's relationship with emotional disorders, interpretations of these relationships become conceptually problematic. More specifically, when the POFs show the strongest predictive power and the GNF shows only weak predictive power (if at all), one could achieve specific prediction for purely applied purposes but N's relationship with emotional disorders may demonstrate little more than a tautology. On the other hand, if the POFs add to the GNF in accounting for N's relationship with their respective emotional disorders but the GNF is the strongest predictor, it will constitute initial evidence for disorder specific prediction while also allowing one to rule out tautology as the sole explanation for N's relationships with those disorders. Finally, if the POFs do not add to a strongly predictive GNF, we could rule tautology as an explanation for N's relationships but we would have no evidence for specificity.
As noted earlier, there is not general agreement about the facets of N. Indeed, the field has not yet reached consensus regarding the facets of any of the Big 5 trait dimensions. Of course, a preliminary criterion for a proposed facet is that it correlates with the general factor underlying the domain that it is hypothesized to be a facet of. A further criterion that might be used in deciding whether a proposed facet should be retained in a consensual model of the facets of a trait is incremental validity. If a hypothesized facet not only correlates with the general factor underlying the domain but also has incremental validity (above and beyond the general factor it is associated with) in predicting a meaningful outcome this would constitute evidence that it is useful to recognize that facet as a subcomponent of its trait dimension. In contrast if many tests of the incremental validity of a hypothesized facet all fail then parsimony would dictate that the items comprising that hypothesized facet be regarded simply as indicators of the general factor associated with the trait rather then being indicators of a meaningful subcomponent of the trait. The hierarchical factor model therefore also provides a useful method for identifying facets that are meaningful to distinguish from their general factors.
Thus, the purpose of this study was to apply a specific statistical model - the hierarchical factor model (e.g., McDonald, 1999
; Zinbarg, Revelle, Yovel & Li, 2005
) - to determine the unique effects of the POFs (the depression and anxiety facets) and the GNF of N in accounting for the established relationship between N and the emotional disorders without deleting potentially overlapping items. In so doing, we aim to avoid compromising the validity of the constructs and hampering the search for disorder specific prediction that might ensue from the removal of overlapping items. An addition aim of this study was to provide initial evidence identifying facets that should be recognized in a consensual model of the subcomponents of N. In so doing, we hope to demonstrate the utility of the hierarchical factor model as a general tool for testing the incremental validity of the facet level constituents of broad personality traits. (In contrast, a higher-order factor model would be much more useful for testing whether a hypothesized facet correlates with a general factor.)