Effects of sample size on the reliability of noise floor and DPOAE

This study investigated the effects of sample size on the test-retest reliability of the amplitude of distortion product otoacoustic emissions (DPOAE) (2f1-f2) and on the noise floor. Four pairs of primary frequencies (fl and f2) with geometric means of 531, 1000, 2000 and 4000 Hz were presented to 55 normal-hearing women at intensity levels of 35, 45 and 55 dB SPL (L1 = L2). Sample sizes of 12, 25, 50, 100, 200 and 400 sweeps were averaged. The results revealed that sample size, frequency, and intensity had little effect on the standard error of measurement. Thus, the DPOAE data were combined across all conditions and yielded a standard error of measurement of 2.2 dB. To assess whether two DPOAE measurements are statistically significant (e.g. before and after drug administration), the standard error of measurement of the difference between two values was calculated (3.1 dB). Thus, by use of the 95% confidence interval, the difference between two DPOAE is statistically significant if it exceeds approximately 6 dB.