FIG. 2.

The standard error of mean (SEM) for adult and newborn estimates of DPOAE level. This intra-subject SEM was calculated for all subjects from repeated sweep-based estimates [see Figs. 1(A) and 1(C)], first in pressure and then converted to dB SPL. This procedure allows for a measure of within-ear stability and provides a metric of response quality for each subject. The group SEM was determined by fitting a loess trend line to the individual functions; it approximates group-noise floor measurements, which are shown as dotted lines. In adults, the group noise floor is within a few dB of the calculated intra-subject SEM. In newborns, within-ear variability is greater than in adults and the SEM is notably higher than the group noise floor suggesting other sources of variance.