Specificity-Enhanced Reliability Coefficients

Internal consistency reliability coefficients based on classical test theory, such as alpha, omega, lambda(4), model-based rho(xx), and the greatest lower bound rho(glb), are computed as ratios of estimated common variance to total variance. They omit specific variance. As a result they are downward-biased and may fail to predict external criteria (McCrae et al., 2011). Some approaches for incorporating specific variance into reliability estimates are proposed and illustrated. The resulting specificity-enhanced coefficients alpha(+), omega(+), lambda(+)(4), rho(+)(xx) and rho(+)(glb) provide improved estimands of reliability and thus may be worth reporting in addition to their classical counterparts. The correction for attenuation, Spearman-Brown, and maximal reliability formulas also are extended to allow specificity. Limitations, future work, and implications are discussed, including the role of specificity to quantify the extent to which items represent important facets or nuances (McCrae, 2015) of content.