Conferences

Including psychological scales and questionnaires in survey questionnaires has become a common practice in the last years. Psychometric concepts and techniques can help survey researchers to improve quality of survey results while particular characteristics of survey research are taken into account. The focus of this paper is the Differential Item Functioning (DIF) analysis. Few studies have been conducted on Differential Item Functioning (DIF) analysis in survey data as compared with DIF research in educational test and psychological questionnaire. When survey purposes involve different cultural and linguistic groups, survey researchers could take advantage of DIF study results in order to make much more solid interpretations of measures rejecting alternative interpretations about lack of functional equivalence. As an empirical example, partial results of polytomous DIF analysis performed on the Spanish version of the General Health Questionnaire will be presented. The Spanish version of the GHQ is included in a national health survey. Polytomous DIF analysis comparing groups defined by a set of demographic variables were conducted by Logistic Regression analysis. Finally, the theoretical convergence between DIF results and evidence provided by qualitative methods will be also discussed.