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Item Response Theory


Admission requirements

Master students Psychology specialisation Methodology and Statistics


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 analysed by classical test theory, but this has its limitations. Over the last decades, modern test theory has gained influence, since it allows us to analyse 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 practised in R, with the predefined ltm package.

Course objectives


  • Acquire knowledge of and insight into the principles of relevant modern test theoretical models and techniques

  • Acquire knowledge of, insight into, and practical competence with respect to analysing 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 (2011-2012)

Mode of instruction

Lectures, software demonstrations, and homework assignments.

Assessment method

The final grade for this course will be based on:

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

  • Written exam

From January 1, 2006 the Faculty of Social Sciences has instituted the Ephorus system to be used by instructors for the systematic detection of plagiarism in students’ written work. 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


Master’s introduction and enrolment day

Make a reservation in your agenda so you will not miss any information that you will need during your master’s programme MSc in Psychology. Please consult the Agenda master meetings

Exam registration

Registration for the (re)exam is not automatic. Students, who haven’t registered, cannot participate in the (re)exam

Contact information

Prof.dr. W.J. Heiser
Room 3B19
Tel: 071-5273828