Accuracy and reliability of a real-ear-to-coupler difference measurement procedure implemented within a...

Measurement of the real ear response of a fitted hearing aid allows matching of the frequency response to prescriptive targets, as well as comparison of the response to both threshold and loudness discomfort level (LDL). These processes are recommended procedures for hearing aid fittings. The real ear aided response (REAR) is often predicted based on the coupler response of the device, the real-ear-to-coupler difference (RECD), and the microphone location effect (MLE). Individualized measurement of the RECD tends to increase the accuracy of this prediction. A commercial hearing aid has been developed that measures the individual RECD and incorporates the data into the software-assisted fitting process.

This study evaluated the test-retest reliability and predictive validity of this particular method for measuring the RECD.

A repeated measures design was used to evaluate differences between subsequent measures of the RECD in the same ear, and prediction differences associated with using the RECD (and other information) to predict the REAR.

Fifteen ears, on a convenience sample of ten adults (45-86 yr) and five children (6-15 yr) were tested. All participants were hearing aid users.

Predicted and measured REARs were collected using normal clinical procedures, on an Audioscan Verifit VF-1 for two test signals/levels. Reliability, mean differences between predicted and measured REARs, and 95% confidence intervals of the prediction accuracy are reported.

The RECD procedure had test-retest reliability within 2.5 dB for 14 out of 15 ears between 500 and 4000 Hz, and had predictive accuracy within 5 dB between 500 and 4000 Hz for 14 out of 15 ears. However, errors associated with earhook misalignment were discovered. Also, the RECD values measured using this hearing-aid-specific procedure differ somewhat from the normative data available from insert earphone RECDs.

This procedure, when measured according to recommendations, provides a reasonably accurate prediction of the REAR. Functionally, this procedure does not replace the range of measures offered by modern real ear measurement systems. However, given the inaccuracy of software-assisted fittings without a measure of individual ear canal acoustics, use of this procedure may have the potential to improve the accuracy of fittings versus fittings completed without real ear measurement.