锚题比例与年级离散度对垂直等值的影响
The Effect of the Ratio of Anchor Items to Total Test and the Separation of Grade Distributions on the Precision of Vertical Scaling

采用锚题设计,选择年级1作为参照基准,通过蒙特卡洛模拟方法,考察锚题比例与年级离散度对垂直等值的影响.研究结果表明:与基准年级的距离影响垂直等值效果,越靠近基准年级,估计精度越好; 从整体而言,垂直等值锚题比例设为30%,等值效果最好; 垂直等值锚题比例的设定受年级离散度影响,2者存在交互作用,锚题比例设为“变”值更好.
The paper aimed at the effect of the ratio of anchor items to total test and the separation of grade distributions on the precision of vertical scaling.The paper used common-item design and chose grade 1 as base grade,by Monte Carlo simulation method simulated the different ratio of anchor items to total test and separation of grade distributions studied the influence of vertical scaling.The result shows that:(i)Selection of base grade affected the precision of vertical scaling.The closer to the base grade,the better the accuracy of the estimate is.(ii)When there is a 30% ratio of anchor items to total test,the precision of vertical scaling is best.(iii)The ratio of anchor items to total test is affect by the separation of grade distributions.There is an interaction between the two,and the ratio of anchor questions is set to "change"