影響積差相關係數與α信度係數之因素

Factors Affect Pearson Correlation and Coefficient Alpha

在教育研究中，相關係數(r)之使用相當頻繁；而編製測驗過程中，α信度係數亦扮演著重要的角色，故本文探討的二個主題包括； (一 ) 影響積差相關係數的因素；(二 )影響α信度係的因素。 影響積差相關係數之因素部分，內容包括五項：(一 )r 之基本假設；線性相關，分配相似性與等分散性；(二 ) 形成假性相關的原因； (三 ) 影響 r 之因素有四：線性；二變項之分配情形；二變項分數之測量誤差與團體之變異量；(四 ) 不會影響r 之因素：變數之線性轉換；(五 )r 之四個特例：φ相關；點二系列相關； 二系列相關和斯皮爾曼等級相關。 影響α信度係數之因素部分，內容包括五項：(一 ) 信度之定義；(二) α係數的意義與特性； (三 ) 內部一致性單一向度與 (四 ) α係數之計算；(五 ) 影響α係數之因素：受試之同質或異質；測驗之長度；題目間之相關；以及試題難度之同質性。

Pearson correlation (r) is employed frequently in educational researchand Cronbach's coefficient alpha( α ) plays animportant role in testconstruction. Two topics were investigated in the article: factors affectPearson r and coefficient alpha. Four issues were included in the part offactors affect r: first， the assumptions under r: linear relationship betweenvariables， similar distribution， and homoscadasticity; second， spuriouscorrelation; third， factors affect r: linearity， distribution of variables，error of measurement， and restriction in range; fourth， factors do not affect r:linear transformation of variables; and fifth， special cases of r: phicorrelation， point-biserial correlation， biserial correlation， and Spearman rankcorrelation. Five issues were discussed in the part of factors affect alpha:first， the definition of reliability; second， the meaning and characteristics ofreliability; third， internal consistency and dimensionality; fourth， thecalculation of coefficient alpha; and fifth， factors affect coefficient alphaincluding: homogeneity or heterogeneity of subjects， the length of a test，interitem correlation， and homegeneity of item difficulty.