SPSS-X Procedure and Standalone Programs for the Mokken Scale Analysis: A Nonparametric Item Response Theory Model

Abstract

A nonparametric item response theory model, the Mokken scale analysis, and program are described. Three scaling procedures are distinguished: a search procedure, the evaluation of the whole set of items, and the extension of an existing scale. All procedures provide a coefficient of scalability for all items that meet the criteria of the Mokken model, and an item coefficient of scalability for every item. Four different types of reliability coefficients are provided, both for the whole set of items and the set of scalable items. In order to analyze whether the established Mokken scale is invariant across different subgroups, a test of robustness is performed by employing a statistic T which approaches a chi-square distribution with p - 1 degrees of freedom (where p is the number of groups to be compared). The robustness test serves as a goodness of fit test for the established scale. The program is written in FORTRAN 77. Two versions are available: An SPSS-X procedure program (which can be used with the SPSS-X mainframe package) and a standalone program suitable for both mainframe and microcomputers.