Are real-ear measurements (REM) accurate when using the modified pressure with stored equalization (MPSE) method?

Audiologists typically verify hearing instrument fitting using real-ear measurements (REM). Recently the modified pressure with stored equalization method (MPSE) has been recommended for use when verifying open non-occluding hearing instruments. The MPSE method does not use a reference microphone to maintain loudspeaker output during real-ear measurements and is therefore susceptible to changes in the signal level at the client's ear which result from movement of the client's head and torso during the verification process. To determine the size of these errors, the real-ear unaided response (REUR) was measured prior to and following the fitting of a non-functioning hearing aid in the contralateral ear. Twenty young adults participated. Identical head positions for the two measurements should yield zero difference measures across all frequencies measured. Loudspeaker-to-client azimuths of 0 degrees and 45 degrees were investigated. Mean difference measures across the frequencies investigated were less than 1 dB for both azimuths with one standard deviation from these mean differences typically less than 1.5 dB. Results suggest that the MPSE method does not introduce clinically significant errors in real-ear measurements when verifying hearing instrument fitting in the population examined.