以無母數檢定法分析資料前後測差異時,該如何呈現差異的大小?換句話說,無母數統計法中是否有同等於效應值 (effect size)的指標?
文獻回顧之結果發現success rate difference (SRD) (Cliff, 1993) 是個常用於無母數統計法中的效應值,又稱為Cliff's dalta。計算方式為probability (scores at admission> index at discharge)- probability (scores at admission> index at discharge)。此值介於-1~1之間,0表示前後測結果沒有差異,越接近1或-1表示前後測知結果差異越大。Kraemer等學者試著換算SRD及Cohen's d,並依照Cohen's d效應值大小的標準(>0.8為大;0.5-0.8為中;0.2-0.5為小),建議SRD值>0.43代表大的改變;0.28-0.43為中度;0.11-0.27為小 (Kraemer & Kupfer, 2006) 。
參考資料:
Cliff,
Norman. (1993). Dominance statistics: Ordinal analyses to answer ordinal
questions. Psychological Bulletin, 114,
494.
Kraemer, Helena Chmura, & Kupfer, David J.
(2006). Size of Treatment Effects and Their Importance to Clinical Research and
Practice. Biological Psychiatry, 59,
990-996.