title: A more nuanced view of reliability: specificity in the trait hierarchy.
abstract: Retest reliability is a better predictor of validity than is internal consistency. One explanation for this is item-specific variance, which distinguishes different nuances of a facet and contributes to retest reliability but not internal consistency. Specific variance at the facet level is temporally stable, consensually validated, and heritable; a consideration of the role of specific variance in personality measures leads to a distinction between traits as the intersection (∩) versus the union (∪) of their constituents. I discuss specific variance at the item level and its implications for scale development and argue that retest reliability outpredicts internal consistency because item-specific variance has been shown to be observable, and is probably heritable and stable. I consider some implications of these ideas for the use of single-item scales, the causal interpretation of traits, and the notion of scalar equivalence. Finally, I note that the sources of random error in scales are still poorly understood.
authors.affiliation: Baltimore, Maryland, USA RRMcCrae@gmail.com.
authors.forename: Robert R
authors.initials: RR
authors.lastname: McCrae
mesh_terms: D006801:Humans; D010551:Personality; D010555:Personality Inventory; D011594:Psychometrics; D015203:Reproducibility of Results; D013223:Statistics as Topic
keywords: Five-Factor Model; consensual validation; reliability; scalar equivalence; scale development