Specificity-Enhanced Reliability Coefficients

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Internal consistency reliability coefficients based on classical test theory, such as α, ω, λ4, model-based ρxx, and the greatest lower bound ρglb, 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 α+, ω+, λ4+, ρxx+ and ρglb+ 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.

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