The Placebo Effect and the Influence of Participant Expectation on Hearing Aid Trials

Objective: The aim of the study was to investigate the influence of participant expectation on the outcome of a trial that compared two behind-the-ear hearing aids with identical electroacoustic performance, except that one was called a "new" hearing aid and the other a "conventional" hearing aid. Design: Twenty experienced adult hearing aid users were told that they were taking part in a trial that compared new and conventional hearing aid technology. They attended a single test session where they were fitted with each hearing aid, in a balanced design, set to the same National Acoustic Laboratories' nonlinear fitting procedure (Version 1) prescription target for a typical age-related hearing impairment. Outcome measures were selected to be representative of hearing aids trials and included (i) the Four Alternative Auditory Feature test (presented at 65 dB (A) and SNR ratio of +2 dB), (ii) sound quality ratings for six different sound samples (a selection of speech, music, and environmental sounds), and (iii) overall personal preference. Results: There was marginally better mean performance with the new hearing aid on the Four Alternative Auditory Feature test (M = 62.3%, SD = 10.4 versus M = 60.7%, SD = 9.0; z = -1.84, p = 0.03, one-tailed, effect size Pearson's r = 0.08; although p = 0.06, two-tailed). The new hearing aid was also consistently rated more highly on all sound quality ratings and this difference was statistically significant (M = 9.12, SD = 1.02 versus M = 8.35, SD 1.17; z = -2.88, p < 0.01, two-tailed, r = 0.33). Fifteen (75%) participants expressed an overall personal preference for the new hearing aid with the remainder expressing no preference (p = 0.02, r = 0.50). Conclusions: These results suggest a need to control for placebo effects in hearing aid trials and to interpret cautiously any hearing aid trial that did not control for this effect.