

Resources 
Item Response Theory is the study of test and item scores based on assumptions concerning the mathematical relationship between abilities (or other hypothesized traits) and item responses. Other names and subsets include Item Characteristic Curve Theory, Latent Trait Theory, Rasch Model, 2PL Model, 3PL model and the Birnbaum model. In the following figure, the xaxis represents student ability and the yaxis represents the probability of a correct response to one test item. The sshaped curve, then, shows the probabilities of a correct response for students with different ability (theta) levels. Modeling the relationships between ability and a set of items provides the basis for numerous practical applications, most of which have advantages over their classical measurement theory counterparts. The goal of this page is to provide resources to help you learn more about this class of measurement models. The main feature of this page is Frank Baker's exceptional book, The Basics of Item Response Theory, which we have made available, in its entirely, online, at no cost. This delightful book will allow you to acquire the basic concepts of the theory without becoming enmeshed in the underlying mathematics and computational complexities. We hope you will take advantage of this important contribution by Dr. Baker.
December
2001


The Basics of Item Response Theory (by Frank Baker)  
Introduction Chapter 1  The Item Characteristic Curve Chapter 2  Models Chapter 3  Estimation of item parameters Chapter 4  Test Characteristic Curve Chapter 5  Ability Estimation Chapter 6  Information function Chapter 7  Test Calibration Chapter 8  Test Characteristics References & Resources Software Complete book(800K) pdf 

Tutorials  
Computer Adaptive Testing
by Lawrence Rudner, ERIC IRT Modeling by University of Illinois IRT Modeling Lab Generate ICC's and Information functions, interactive IRT Overview by Penn State University testing Services 

Other IRT sites  
Institute for
Objective Measurement, Inc.Excellent
comprehensive site for the Rasch model University of Illinois IRT Modeling Lab website. Good tutorial. UMD. Under development featuring an unfolding model. 

Paper Collections on IRT  
Rash
Measurement Transactions MD Assessment Archive 

Software (free)  
PARAM3PL Calibration for the 3PL IRT Model
 Via Larry Rudner, GMAC IRT Programs and Datasets  Via IRT Modeling Lab, UIUC Rasch  Via Winsteps Unfolding  Via Jim Roberts, UMD Some source code 

Software (via Assessment Systems Inc)  
PARSCALE
Performs IRT scaling, item analysis, and scoring of rating scale
data. BILOGMG Estimates IRT parameters for multiple groups, allowing detection of differential item functioning. MULTILOG Provides versatile multiplecategory IRT analysis for polytomous IRT models. XCALIBRE Marginal maximumlikelihood IRT parameter estimation with small numbers of examinees or short tests, for the 2 and 3parameter IRT model. 

Books (via amazon.com)  
Item Response Theory: Parameter Estimation Techniques, Second
Edition  by Frank Baker and SeockHo Kim Item Response Theory for Psychologists  by Susan E. Embretson and others Essays on Item Response Theory by Anne Boomsma (Editor) Handbook of Modern Item Response Theory by Wim J. Van Der Linden & Ron Hambleton (Editors) Computerized Adaptive Testing by Howard Wainer and others Fundamentals of Item Response Theory by Ronald Hambleton Error Free Mental Measurements by Robert M. Hashway (in press) Test Scoring by David Thissen & Howard Wainer (Editors) Applying the Rasch Model by Trevor G. Bond, Christine M. Fox 