影響α內部一致性係數的因素

SOME FACTORS AFFECTING CRONBACH'S ALPHA

Cronbach's α公式自從1951提出以後，40幾年來一直被研究者用來作為問卷內部一致性的指標。本研究探討題目數目、各題共變關係與變異數差異情形，與問卷因素結構等三個因子對Cronbach's α可能造成的影響。根據本文對該係數公式的分析與電腦模擬，這三個因子都會對係數產生影響。這些影響勢將改變一般研究者對於Cronbach's α的傳統認識，並澄清α公式在問卷編製裡的意義。研究者在不得不需使用α係數的情況下，也應瞭解並提醒讀者這些因素會造成的影響，否則所得係數值將難以具有明確意義。

This article evaluates the practical usefulness of Cronbach's α formula which has been adopted by many reseachers in their test construction as an index of internal consistency without serious considerations until now especially in Chinese. Using simple arithmetic deduction and monte carlo experiments, three factors including numbers of items,item heteroscedasticity, and underlying factor structure, were shown to exert influence upon the magnitude of alpha coefficient in such a degree that the theoretical significance of alpha will be largely questioned and should be used with caution.