Evaluation of the International Outcome Inventory for Hearing Aids in a veteran sample.

BACKGROUND The International Outcome Inventory for Hearing Aids (IOI-HA) was developed as a global hearing aid outcome measure targeting seven outcome domains. The published norms were based on a private-pay sample who were fitted with analog hearing aids. PURPOSE The purpose of this study was to evaluate the psychometric properties of the IOI-HA and to establish normative data in a veteran sample. RESEARCH DESIGN Survey. STUDY SAMPLE The participants were 131 male veterans (mean age of 74.3 years, SD = 7.4) who were issued hearing aids with digital signal processing (DSP). INTERVENTION Hearing aids with DSP that were fitted bilaterally between 2005 and 2007. DATA COLLECTION AND ANALYSIS Veterans were mailed two copies of the IOI-HA. The participants were instructed to complete the first copy of the questionnaire immediately and the second copy in two weeks. The completed questionnaires were mailed to the laboratory. The psychometric properties of the questionnaire were evaluated. As suggested by Cox and colleagues, the participants were divided into two categories based on their unaided subjective hearing difficulty. The two categories were (1) those with less hearing difficulty (none-to-moderate category) and (2) those who report more hearing difficulty (moderately severe+ category). The norms from the current veteran sample then were compared to the original, published sample. For each hearing difficulty category, the critical difference values were calculated for each item and for the total score. RESULTS A factor analysis showed that the IOI-HA in the veteran sample had the identical subscale structure as reported in the original sample. For the total scale, the internal consistency was good (Chronbach's alpha = 0.83), and the test-retest reliability was high (lambda = 0.94). Group and individual norms were developed for both hearing difficulty categories in the veteran sample. For each IOI-HA item, the critical difference scores were < 1.0. This finding suggests that for any item on the IOI-HA, there is a 95 percent chance that an observed change of one response unit between two test sessions reflects a true change in outcome for a given domain. CONCLUSIONS The results of this study confirmed that the psychometric properties of the IOI-HA questionnaire are strong and are essentially the same for the veteran sample and the original private-pay sample. The veteran norms, however, produced higher outcomes than those established originally, possibly because of differences in the population samples and/or hearing aid technology. Clinical and research applications of the current findings are presented. Based on the results from the current study, the norms established here should replace the original norms for use in veterans with current hearing aid technology.