Page 18 - Fall2013

Shargorodsky et al used an unselected sample of the NHANES data for their analysis and these survey data were not collected with the same rigor as the laboratory methods used to define the reference values for dB HL (Schlauch and Carney, 2012). In Shargorodsky et al.’s cohort, children with conditions that are known to elevate thresholds, such as abnormal middle-ear function (such as with otitis media) or impacted earwax, were not excluded from their analysis. At the time the NHANES audiograms were collected, partici- pants’ middle ear function was assessed and otoscopy was performed. Schlauch and Carney (2012) performed an inde- pendent analysis of the NHANES 2005-2006 data (the same data that Shargorodsky et al. used in their study) and exclud- ed persons who had abnormal middle-ear function, abnor- mal otoscopy, or any other factor that could have affected thresholds that is unrelated to NIHL. We found that only 6% of 12-19 year old children had high-frequency losses (with no low-frequency component).
Selecting the boundary (cut off) between “normal hearing” and “hearing loss”
Another concern with Shargorodsky et al.’s analysis is the cut off for normal hearing. An examination of the audio- grams from the selected group in our analysis of the NHANES teens judged to be otologically normal showed that their average thresholds were between 5 and 10 dB HL at each frequency rather than 0 dB HL, the expected value.
Given these elevated average thresholds in the otologically normal group and the known variability of pure-tone audiometry, 15 dB HL is too low a cut-off to define the bound- ary between normal hearing and hearing loss. This is particu-
Figure 3. Examples of simulated, flat audiograms labeled as having high-frequency notches using criteria proposed by Niskar et al. (2001). These deviations from a flat a audiogram represent “false positive” notches that reflect variability caused by the imprecision of pure tone audiometry. For illustration purposes, the mean value for the flat audiogram that was the input to the simulation was fixed at either 0 dB HL or 7.5 dB HL rather than drawn from a normal distribution
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Hearing Loss in Teenagers 17
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