因年齡組骨齡讀數(shù)為非正態(tài)分布,呈現(xiàn)出不同程度的偏度與峰度,所以應(yīng)用適用于偏態(tài)和峰態(tài)分布數(shù)據(jù)的Box-Cox冪指數(shù)分布模型[7](Box-Cox power exponential distribution,BCPE),估價(jià)以不同方法評(píng)價(jià)的骨齡百分位數(shù),采用三次樣條函數(shù)擬合百分位數(shù)曲線,比較骨齡分布與年齡的關(guān)系。以兩相關(guān)樣本的非參數(shù)檢驗(yàn)(Two-Related-Samples Test),檢驗(yàn)不同方法骨齡間的差異,檢驗(yàn)的類(lèi)型為符號(hào)秩和檢驗(yàn)(Wilcoxon Signed Ranks Test)。
各骨齡分布的BCPE模型參數(shù)見(jiàn)表1,λ為年齡的冪轉(zhuǎn)換參數(shù),df(μ)、df(σ)、df(ν)和df(τ)分別為骨齡分布的位置(中位數(shù))、尺度(變異系數(shù))、偏度(Box-Cox轉(zhuǎn)換冪)和峰度(冪指數(shù)參數(shù))參數(shù)的自由度(degrees of freedom, df)。圖1,圖2為以表1中各BCPE模型參數(shù)所繪制的骨齡百分位數(shù)曲線圖。
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