An examination of several characteristics that affect the prediction of OSPL90 in hearing aids

Objective: Investigators at the National Acoustic Laboratories have provide d a theoretical derivation and experimental validation of a formula for set ting the maximum output of hearing aids (Dillon & Storey, 1998; Storey, Dil lon, Yeend, & Wigney, 1998). Given that measurement of discomfort levels fo r setting maximum output can be both time-consuming and of questionable rel iability, the use of a prescriptive formula warrants consideration. In this article, an extensive data base was considered and issues of normal hearin g, clinical protocol, age and gender were investigated in an effort to furt her determine optimal maximum output settings. Design: Data were gathered from five previous investigations, for a total o f 433 subjects (total ears 710). Threshold of discomfort (TD) measures were obtained using one of two adaptations of the Ascending Method of Limits, o ne with category anchors and one without. Results: Subjects with normal hearing had significantly lower TDs than subj ects with hearing loss. A different, regression line for measured TDs as a function of hearing level was noted for subjects whose hearing threshold le vels fell between 20 and 60 dB HL and those with thresholds above 60 dB HL. When all effects (hearing level, method, age and gender) were considered i n a single predictive model for the two threshold groups, only method and t hreshold were significant predictors of TD. However, for the subjects with thresholds between 20 and 60 dB HL, less than 4% of the variance in TD meas ures could be accounted for by those factors. For subjects with threshold a bove 60 dB HL, 22% of the variance in TD measures could be accounted for by those variables. Conclusions: For both groups of subjects (20 to 60 dB HL and above 60 dB HL ) methodology and hearing thresholds are significant predictors of discomfo rt levels. Age and gender are not. Given the small variance accounted for b y any of these factors, measures of discomfort using standardized methodolo gies seem warranted.