Assessing Validity of Measurement in Learning Disabilities Using Hierarchical Generalized Linear Modeling.

The purpose of the present studies was to test the hypothesis that the psychometric characteristics of ability scales may be significantly distorted if one accounts for emotional factors during test taking. Specifically, the present studies evaluate the effects of anxiety and motivation on the item difficulties of the Rasch model. In Study 1, the validity of a reading comprehension scale was evaluated using the Rasch model with 60 students with learning disabilities (LD). Item parameters were retested for the presence of anxiety and results indicated that the scale was substantially more difficult in its presence. Study 2 replicated the findings of Study 1 using maladaptive motivation and extended with inclusion of adaptive motivational variables in order to reverse the effect. Results using students with and without LD indicated that the difficulty levels of the scale was lower for students with LD, in the presence of positive motivation, compared with a typical student group. Study 3 extended the dichotomous hierarchical generalized linear model with polytomous data. The measures of an ability test were adjusted for the presence of anxiety and results indicated that differential item functioning was observed at both the global level and the most difficult ability item. It is concluded that the difficulty levels of a scale are heavily influenced by situational factors during testing, such as students’ entry levels of motivation and affect. [ABSTRACT FROM AUTHOR]