本研究主要目的在探討使用三參數logistic IRT模式情形時,定錨試題的分佈對於測驗等化的影響。本研究實驗設計主要控制變因有:1.定錨試題數2.鑑別度參數3.難度參數4.能力值分佈,使用之等化及能力估計軟體為BILOG-MG。 在本研究中探討定錨試題鑑別度參數為0.5、1.0、1.5等三種情形之等化效果,研究結果發現在定錨試題的鑑別度參數為1.0和1.5的等化效果較為理想,在定錨試題難度參數方面,研究結果發現最佳選擇會因定錨題數及受試者能力分佈不同而異。在定錨試題數方面,使用定錨試題愈多且分佈適當,則進行等化估計時愈精準。
The purpose of this study is to investigate the effects of different anchor item distributions on test equating using the 3 parameter logistic model in BILOG-MG. The impacts of four factors will be discussed: 1:the number of anchor item, 2:discrimination parameter of anchor item, 3:difficulty parameter of anchor item, 4:the distributions of ability. Three cases of discrimination parameter of anchor item (a=0:5, 1:0, 1:5) are discussed in this study and the simulation experiment result show that a=1:0 and 1:5 cases have better performances. The result also shows that the best decision of the locations (difficulty parameters) of anchor items depends on the number of anchor items and the ability distributions.