The assessment of DIF on Rasch measures with an application to job satisfaction

The present study addresses the issue in assessment of the impact of differential item functioning on the measures obtained applying the Rasch model when the questionnaire is formed by polytomous items. An item is said to display differential item functioning when it behaves differently among different groups of respondents (for example males and females). A simulation study is used in order to deal with the issue. A differential item functioning analysis is performed making use of a real database concerning the Survey on Italian Social Cooperatives carried out in 2007.