|irt item information function||0.16||0.6||1557||89|
What is IRT? Item response Relationship Sigmoid Function is a type of logistic function .What is Item Response Theory of IRT?
This is in sharp contrast to classical test theory, where such an examinee would get a high test score on the easy test and vice versa Under item response theory, the examinee’s ability is fixed and invariant with respect to the items used to measure it. 56 The Basics of IRT September 9, 2009 57.What is the information function of an item?
The Information Function An item measures ability with greatest precision at the ability level corresponding to the item’s difficulty parameter. The amount of item information decreases as the ability level departs from the item difficulty and approaches zero at the extremes of the ability scale.How to estimate item parameters in IRT?
Estimating Item parameters • Find ICC that best fits the observed proportions of correct response. •first select a model for the curve to be fitted. • Let’s fit 2PL (chi-square goodness-of-fit index to assess fitness) • Procedure is Maximum Likelihood Estimation (initial values b=0,a=1) 34 The Basics of IRT September 9, 2009