Method biases in single-source personality assessments

The magnitude of components of variance in trait scales-true score, method variance, and error-can be estimated from information on the mono-method correlations among personality traits within a domain and on cross-observer agreement on domains and facets. Estimates of these components in NEO Inventory facet scales were compared with prior estimates that were based on a consideration of internal consistency and retest reliability (McCrae, 2015). Together, results suggested that (a) about 40% of the variance in self-reports and single informant ratings is due to method variance; (b) as with substantive traits, method biases exist on several different levels, some broad, some narrow; and (c) consequently, a large number of distinct biases affect personality scale scores. Method biases beyond acquiescence and evaluation were also found in a clinical instrument, the Personality Inventory for DSM-5. Because many biases appear to be idiosyncratic, it is unlikely that validity scales could be created to assess or control all of them. These findings underscore the value of utilizing multiple informants in research and individual assessment. To the extent that they can be distinguished from valid variance, method biases are themselves of clinical interest as potentially important elements of the self-concept. (PsycINFO Database Record