Greer Tammy, Dunlap William P, Hunter Samuel T, Berman Mitchell E
Department of Psychology, The University of Southern Mississippi, Hattiesburg, MS, USA.
J Appl Psychol. 2006 Nov;91(6):1351-8. doi: 10.1037/0021-9010.91.6.1351.
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.
采用蒙特卡罗技术检验了偏态对标准化项目α系数的影响。将从正态变量计算出的α系数与对数正态变量、秩以及偏态与正态李克特型变量的α系数进行比较。偏态的程度和方向有所变化，总体项目间相关性（ρ）的大小、项目数量以及李克特型变量的类别数量也有所不同。由于平均项目间相关性会影响α系数，而偏态会影响平均项目间相关性，因此也检验了偏态对平均项目间相关性的影响。结果表明，偏态降低了平均项目间相关性，并使α系数略有下降，当偏态较大、ρ较小时，项目呈相反方向偏态且项目数量较少时，α系数下降幅度最大。
