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Item Response Theory


Admission requirements

Master students Psychology specialisation Methodology and Statistics. Psychology Research Master students are also admitted.


In psychological research, it is often needed to measure latent person characteristics such as mathematics ability, anxiety, and attitude towards political issues. Tests and test scores play an important role. Traditionally, test scores were analyzed by classical test theory, but this has its limitations. Over the last decades, modern test theory has gained influence, since it allows us to analyze the data on the item level and to develop and test a measurement scale of item responses (Item Response Theory models or IRT).

This course offers a theoretical and practical introduction to IRT models. IRT principles are contrasted with CTT principles. Several IRT models are discussed: those for dichotomous item responses (e.g., right/wrong; agree/disagree) and those for categorical responses (e.g., wrong/partially correct/completely correct; multiple choice options). In each of these models, the probability of answering a particular response category is related to the latent characteristic or the latent trait, in a nonlinear way. Several applications of IRT are discussed, including how to calibrate a measurement scale, how to obtain person estimates and how to interpret them, how to find out whether all items ‘work’ the same way for different groups of test takers (differential item functioning), how to compare scores measured on similar but different tests (test equating), and how to make use of computers to make tests shorter (computerized adaptive testing). Several analyses will be practiced in R, mostly with the predefined ltm package but other packages are also used.

Course objectives


  • Acquire knowledge of and insight into the principles of relevant modern test theoretical models and techniques, also compared to classical test theory

  • Acquire knowledge of, insight into, and practical competence with respect to analyzing test data with IRT models

  • Acquire knowledge of and insight in several issues in applications of IRT to different fields of psychology


Item Response Theory (2014-2015)



Students need to enroll for lectures and work group sessions. Please consult the Instructions registration


Students are not automatically enrolled for an examination. They can register via uSis from 100 to 10 calendar days before the date; students who are not registered will not be permitted to take the examination. Registering for exams

Mode of instruction

Eight lectures (2 hours each) including software demonstrations. Homework assignments that are discussed at the beginning of the next lecture.

Assessment method

The final grade for this course will be based on:

  • Two graded assignments: 1 halfway the course and 1 final assignment.

  • One written exam

The Faculty of Social Sciences has instituted that instructors use a software programme for the systematic detection of plagiarism in students’ written work. In case of fraud disciplinary actions will be taken. Please see the information concerning fraud


Information on

Reading list

  • Embretson, S. E. & Reise, S. P. (2000). Item Response Theory for Psychologists. Mahwah, NJ: Lawrence Erlbaum Associates, Inc. ISBN10: 0805828192. Approximately €40 – €50.

  • Rizopoulos, D. (2006). ltm: An R package for latent variable modeling and Item Response Theory Analysis. Journal of Statistical Software, 17(5), 1–25. Can be downloaded from

Contact information

Dr. M. Hickendorff
Room 3B18
Tel: 071-5273765