Fit-to-Targets and Aided Speech Intelligibility Index Values for Hearing Aids Fitted to the DSL v5-Adult Prescription

Matching hearing aid output levels to prescribed targets is a component of preferred practice, yet recent normative data on appropriateness of fittings are lacking. Verification measures that assess closeness of fit-to-target include raw deviations from target, root-mean-squared-error (RMSE) deviations from target, and aided Speech Intelligibility Index (SII) values. Establishing normative ranges for these measures may help hearing professionals determine whether a patient's fit-to-targets and/or aided speech audibility is typical for his or her degree of hearing loss.

This article aims to characterize the range of fit-to-target and the range of aided SII associated with hearing aid fittings using the Desired Sensation Level version 5.0 (DSL v5-adult) prescription with adults, considering also hearing aid style, venting, and audiometric characteristics.

A descriptive and correlational study of data collected from a retrospective chart review.

Hearing aid fittings to 281 ears were compiled. The four-frequency average deviation from target (RMSE) was within ± 5 dB of target in 77% of fittings for mid-level speech. Deviation from targets increased with hearing loss, particularly when the loss is greater than 85 dB hearing level or if the loss was steeply sloping. Venting increased the deviation from targets in the low frequencies. Aided SII values strongly correlated with the participants' hearing thresholds. Clinical ranges for RMSE and aided SII were developed for characterization of fitting outcomes.

Fitting to DSL v5-adult targets was observed within ± 5 dB absolute deviation, or within 5 dB RMSE, on average for typical adult hearing aid fittings. Confidence intervals for deviation from target and aided SII are proposed.