Skew and internal consistency.
The effects of skew on the standardized item alpha were examined with Monte Carlo techniques. Alphas computed from normal variables were compared with alphas from lognormal variables, ranks, and skewed versus normal Likert-type variables. The extent and direction of skew were varied, as was the size of the population interitem correlation (rho), the number of items, and the number of categories for Likert-type variables. Because the average interitem correlation affects alpha and skew affects the average interitem correlation, the effect of skew on the average interitem correlation also was examined. Results indicated that skew decreased the average interitem correlation and produced small decreases in alpha that were largest when skew was large, rho was small, items were skewed in opposite directions, and there were fewer items.
Greer
Tammy
T
Department of Psychology, The University of Southern Mississippi, Hattiesburg, MS, USA. tammy.greer@usm.edu
Dunlap
William P
WP
Hunter
Samuel T
ST
Berman
Mitchell E
ME
D006801:Humans; D008960:Models, Psychological; D009010:Monte Carlo Method; D011584:Psychology / Q000379:methods / Q000706:statistics & numerical data*; D015203:Reproducibility of Results