In addition to the five broad dimensions, future research should examine the specific facets (or lower-order traits) that compose each factor. The facets describe more specific and narrow phenotypes, which might be more easily linked to genetic variants. In fact, although facets tend to covary, a high score on the broad factor can result from the effect of different facets across individuals. For example, among those who score high on Neuroticism, some might score high on anxiety but not depression, whereas other might score high on depression but not anxiety. This phenotypic variability increases noise and reduces the likelihood of identifying genetic variants. There is less phenotypic variability associated with the narrower phenotype assessed by facets, which should provide more power for GWA scans. However, analyses of multiple facets increase the number of tests and the risk of false positives.
