The use of cumulative distributions to determine critical values and levels of confidence for clinical distortion product otoacoustic emission measurements

Distortion product otoacoustic emission (DPOAE) input/output functions were measured at nine f₂ frequencies ranging from 500 to 8000 Hz in 210 normal-hearing and hearing-impaired subjects. In a companion paper [Stover et al., J. Acoust. Soc. Am. 100, 956-967 (1996)], L₁-L₂ was held constant at 10 dB, and L₂ was varied from 65 to 10 dB SPL in 5-rib steps. Based upon analyses using clinical decision theory, it was demonstrated that DPOAE amplitudes for 65/55 dB SPL primaries (L₁/L₂) and DPOAE thresholds resulted in the greatest separation between normal and impaired ears. In this paper, the data for these two conditions were recast as cumulative distributions, which not only describe the extent of overlap between normal and impaired distributions, but also provide the measured value (i.e., the specific DPOAE amplitude or threshold) for any combination of hit and false alarm rates. From these distributions, confidence limits were constructed for both DPOAE amplitude and threshold to determine the degree of certainty with which any measured response could be assigned to either the normal or impaired population. For these analyses, DPOAE measurements were divided into three categories (a) response properties that would be unlikely to come from normal ears, (b) response properties that would be unlikely to come from impaired ears, and (c) response properties for which hearing status was uncertain. Based upon DPOAE amplitude measurements, the region of uncertainty, defined between the 95 percentile for impaired ears and the 5 percentile for normal ears, was relatively narrow for f₂ frequencies ranging from 707 to 4000 Hz. For DPOAE thresholds, this region was relatively narrow for f₂ frequencies ranging from 1414 to 4000 Hz.