The Study of the Accuracy and Consistency of a Series of IRT Observed Score Equatings Using Various Scale TransformationMethods

使用不同量尺轉換法下IRT 觀察分數等化法的精確性和一致性研究

為了評估等化法的精確性和一致性，本研究使用模擬資料，探討不同量尺轉換法下IRT 觀察分數等化法的比較。本研究檢視分開和部分同時（concurrent）試題參數估計、特徵曲線（characteristic curve）和動差量尺（moment scale）轉換法及連鎖等百分比（chained equipercentile， CE）方法等一系列等化方法的結果。此外，研究也比較直接等化（direct equating）〔新卷直接等化到基準卷（base form）〕與間接等化（indirect equating）〔新卷透過一些中介卷（intermediated forms）等化到基準卷〕的等化結果。研究結果顯示：(1)在不同試題參數與量尺轉換方法中，IRT 觀察分數等化法是一致的；(2)直接等化函數和間接等化函數具有相同的精確性與一致性；(3)除了在接近底層與上層的分數外，CE 等化和IRT 觀察分數之等化函數具有相同的精確性與一致性。

In order to evaluate equating accuracy and consistency， a chain of IRT observed score equatings were compared over different scale transformation approaches using simulated data. The study examined a series of equating results from separate and partial concurrent item parameter estimation， the results from the characteristic curve and the moment scale transformation methods， and the results from the chained equipercentile (CE) method. In addition， the study also compared the results from equating a new form directly to the base form (direct equating) to the results from equating the new form indirectly to the base form through some intermediated forms (indirect equating). The study showed: (i) IRT observed score equatings were consistent over different approaches to item parameter estimation and scale transformation; (ii) Direct equating functions were as accurate and consistent as indirect equating functions; (iii) The CE equating functions were as accurate and consistent as the IRT observed score equating functions at most score levels except the scores near the bottom and top levels.