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Item Response Theory


Entry requirements

Only open to master’s students in Psychology with specialisation Methodology and Statistics and research master’s students Psychology.


In psychological research, it is often necessary 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 as 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 such as dichotomous item response models (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 has a nonlinear relationship to the latent characteristic or the latent trait. Several applications of IRT are discussed, including how to calibrate a measurement scale, how to obtain person estimates and how to interpret estimates, 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 IRT analyses will be practiced in R, mostly with the predefined ltm and lme4 packages but other packages may also be used.

Course objectives

Students will acquire knowledge of and gain insight into:

  • The principles of relevant modern test theoretical models and techniques;

  • How item response models and techniques compare to those applied in classical test theory;

  • Practical skills required to analyze test data with IRT models; and

  • Several issues in applications of IRT to different fields of psychology and education.


For the timetables of your lectures, work groups and exams, please select your study programme in:
Psychology timetables



Students need to enroll for lectures and work group sessions.
Master’s course 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

8 2-hour lectures including software demonstrations. Homework assignments are provided after each lecture and discussed at the beginning of the next lecture.

Assessment method

The final grade for this course is based on one oral and two written assignments (40%) and a written exam (60%).

The Faculty of Social and Behavioural 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.

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.

  • Additional texts will be made available on Blackboard.

Contact information

Dr. Claire Stevenson