Photo of Klaas Sijtsma
  • Prof. Cobbenhagenlaan 225, Simon Building, room S 712

    5037 DB Tilburg


1982 …2020
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Personal profile

Research interests

My scientific interest concentrates on the measurement of individual differences with respect to psychological constructs. Reliable and valid measurement is a conditio sine qua non for the usefulness of any psychological variable that reflects an underlying construct. Obviously, this requirement generalizes to any area of scientific research in which multi-item instruments measure underlying constructs, such as in education, marketing, medicine and health, opinion and policy research, political science, and sociology. Without high-quality measurement, in research the data cannot answer the researcher's questions, and in measurement applications students, job applicants and clinical patients cannot be validly assessed. My research covers topics such as reliability of measurement and scalability of stimuli; the definition and investigation of the theoretical properties of modern measurement models known as item response models, both for dichotomous and polytomous item response data; goodness-of-fit investigation of such models; person-fit analysis of patterns of item scores; and item selection aimed at constructing useful measures. Part of my research deals with problems in test and questionnaire data, in particular the analysis of missing item scores and the detection of outliers. The cognitive processes that lead to the responses to items have been the topic of several projects, while another part of my research supports the construction of tests and questionnaires for use in practical applications. I am co-author of two textbooks on measurement that aim to educate graduate students, PhD's and researchers in the area of measurement and psychometrics, and have published approximately 200 articles and book chapters. Many articles have appeared in journals such as Applied Psychological Measurement, Assessment, British Journal of Mathematical and Statistical Psychology, Multivariate Behavioral Research, Psychological Methods, and Psychometrika.

External positions

(Cito b.v.)

1 Jan 201331 Dec 2016

(Commissie Testaangelegenheden Nederland)

1 Jan 2004 → …

(Psychometrie Society)

1 Jul 2003 → …

(Psychometric Society)

1 Jul 2002 → …

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Research Output 1982 2020


Sijtsma, K. & van der Ark, L. A., 2020, (Accepted/In press) Encyclopedia of personality and individual differences. Zeigler-Hill, V. & Shackelford, T. K. (eds.). New York: Springer

Research output: Chapter in Book/Report/Conference proceedingEntry for encyclopedia/dictionaryScientificpeer-review

Item-score reliability: Estimation and evaluation

Zijlmans, E. A. O., 2019, Enschede: Gildeprint. 109 p.

Research output: ThesisDoctoral ThesisScientific

Open Access
earning a doctorate
human being
1 Downloads (Pure)

Item-score reliability as a selection tool in test construction

Zijlmans, E. A. O., Tijmstra, J., van der Ark, L. A. & Sijtsma, K., 2019, In : Frontiers in Psychology. 2018, 9, 12 p., 2298.

Research output: Contribution to journalArticleScientificpeer-review

Open Access
Patient Selection

Longitudinal associations between trait neuroticism and negative daily experiences in adolescence

Borghuis, J., Bleidorn, W., Sijtsma, K., Branje, S., Meeus, W. H. J. & Denissen, J. J. A., 2019, (Accepted/In press) In : Journal of Personality and Social Psychology.

Research output: Contribution to journalArticleScientificpeer-review

human being

Nonparametric item response theory and Mokken scale analysis, with relations to latent class models and cognitive diagnostic models

van der Ark, L. A., Rossi, G. & Sijtsma, K., 2019, (Accepted/In press) Handbook of diagnostic classification models : State of the art in modeling, estimation, and applications. von Davier, M. & Lee, Y-S. (eds.). New York: Springer

Research output: Chapter in Book/Report/Conference proceedingChapterScientific