An Investigation of Measurement Equivalence in Hearing Response Scales: Refinement of a Questionnaire for Use in Hearing Screening

Purpose: Questionnaires used in hearing screening should be short and demonstrate measurement equivalence across groups defined by hearing impairment and hearing aid experience. The measurement equivalence of 2 scales addressing functionality (experienced hearing ability) and social hearing (social barriers due to hearing problems) was investigated. Method: Measurement equivalence was assessed using the differential item functioning and differential test framework within item response theory. Three comparisons were considered: (a) persons with normal hearing versus persons with hearing impairment either owning or not owning a hearing aid; (b) hearing aid users versus individuals who do not use hearing aids; (c) hearing aid users versus persons with hearing impairment who do not use a hearing aid. A protocol of differential item detection was applied consisting of ordinal regression and the log-likelihood ratio test to flag suspect items, followed by applying the log-likelihood ratio test using anchor items (items not suspect of differential item functioning). Results: The 11-item functionality scale was reduced to 9 items, whereas the 10-item social hearing scale was reduced to 7 items. Conclusions: Applying the differential item functioning framework resulted in shorter questionnaires displaying measurement equivalence relative to hearing impairment and hearing aid use without loss of reliability.