# Risk Factors for Distortion Product Otoacoustic Emissions in Young Adults
## 4 Discussion  
In this study of over 200 young adults with normal hearing, almost 35% reported listening to a PM system with earphones at a loud or very loud volume while almost 25% reported that when using a PM system, they had a lot of trouble or could not hear people. In a quiet background environment, however, the mean preferred listening level, measured with a probe microphone over one hour, was below what would be considered hazardous although the maximum level measured in our sample was 97.5 dBA. Lastly, over 70% of participants reported drinking in the last month which is higher than  
Figure 6: **(a)** The means and standard deviations are shown for DPOAE levels across the frequencies tested in women only by Risk categories. ; **(b)** The means and standard deviations are shown for DPOAE levels across the frequencies tested in men only by Risk categories. national estimates of 30-day self-reported alcohol consumption (62%) among college students [18]. Overall, young adult men had higher percentages of self-reported: loud or very loud volume use; having a lot of trouble or cannot hear people; heavy drinking (>14 drinks); and a higher mean preferred listening level compared to women. The mean preferred listening level for all participants was 73.0 dBA and this is consistent with what other researchers have reported for a quiet background condition [7; 9; 10]. Further young adult men in the current study had a statistically significant higher preferred listening level than women, which has been reported previously [7; 10]. Few participants (25 of 216, 11.6%) listened to music >85 dBA which is most likely a result of listening in a quiet background and not having to compete with extraneous noise. Further, this music exposure was one hour and together the measured preferred listening level would not be considered hazardous; although the maximum preferred listening level obtained in the current study would be considered hazardous from a NIOSH perspective [11]. Men that reported loud or very loud volume during PM system use had statistically significant poorer DPOAEs at 1.5, 2, and 3 kHz compared to men that reported low or medium volume use. For women, though, self-reported volume use was not associated with DPOAE levels. [PERSON] et al. [27] found that in a large sample of young adults, those who reported listening to a PM system at maximum or near maximum volume had statistically significant lower DPOAEs at 1.5, 2, 3, and 4 kHz compared to those who reported listening at other volumes. Those general findings are consistent with the current study although [PERSON] et al. [27] did not present sex-specific DPOAE data so it is not clear whether or not those data include sex-specific significant differences like the current study. Most researchers have reported significantly lower DPOAEs in PM system users compared to non-users [13; 28] although recruiting verifiable control participants might be problematic given the very high prevalence of PM system use among young adults [1; 2]. Further, some reported poorer DPOAEs in those who reported more hours of PM system use per week [13] although more recently [PERSON] et al. [14] did not report a weekly use effect on DPOAEs and [PERSON] et al. [15] reported that years of PM system use was not significantly associated with poorer DPOAEs. For women, DPOAEs were similar for the three DPM categories. For men, however, there was a trend indicating poorer DPOAEs at 1.5, 2, and 3 kHz in men who reported any drinking relative to men who reported no past month drinking. The empirical evidence linking alcohol consumption to hearing is limited but one study with a small sample size (\(n=8\)) found statistically significant mean decreases in higher frequency (i.e., 5.5 and 6.6 kHz) DPOAEs after 30 min and 1-h post alcohol consumption [29]. Mean DPOAE levels at these frequencies recovered to pre-consumption levels after 2 h. There were only negligible, non-significant mean changes in DPOAE levels from 0.7 to 4.4 kHz after alcohol consumption. An important finding from [PERSON] et al.