Psychological tests are used in many fields, including medicine and education, to assess the cognitive abilities of test takers. According to international standards for psychological testing, psychological tests are required to be reliable, fair, and valid. This presentation illustrates how R can be used to assess the reliability, fairness, and validity of psychological tests using the Tower of London task as an example. In clinical neuropsychology, the Tower of London task is widely used to assess a person’s planning ability. Our data consist of 798 respondents who worked on the 24 test items of the Tower of London – Freiburg Version. By employing the framework of factor analysis and item response theory, it is demonstrated that the number of correctly solved problems in this test can be considered as a reliable and sound indicator for the planning ability of the test takers. It is further demonstrated that the individual problem difficulties remain stable across different levels of age, sex and education, which provides evidence for the test’s fairness. All computations were carried out with the R packages psych, lavaan and eRm, all of which are freely available on CRAN.
