# Risk Factors for Distortion Product Otoacoustic Emissions in Young Adults
## 2 Materials and Methods
### Measures  
A section of this survey included demographic questions of sex, age, ethnicity, race, and questions specific to PM system use. If the participant answered \"No\" to the question, \"Do you listen to a personal music system using earphones?\" then that part of the survey was not completed. If \"Yes\", then additional questions regarding the type of earphone used, typical duration of listening, longest single use during the day, most common volume used, and if they noticed any problems (e.g., ringing, hearing loss) after using a personal music system were completed. Two of the closed-set survey questions of interest in this study were: \"For a typical day, what is the most common volume used during this day?\" \"Low\", \"Medium/Comfortable\", \"Loud\", or \"Very Loud\"; and \"Do you listen to your personal music system at a volume where you... \" \"Easily hear people\", \"Have a little trouble hearing people\", \"Have a lot of trouble hearing people\", or \"Cannot hear people\". Alcohol use was determined as part of The Risk Factors Survey. For the alcohol questions, a drink was defined as 12 ounces of beer, 5 ounces of wine, or one shot of liquor or a drink containing liquor. These alcohol questions were included from ones developed from a National Institute on Alcohol Abuse and Alcoholism task force that generated recommended sets of alcohol consumption questions [24]. Participants who indicated alcohol consumption during the past 30-days were asked to \begin{table}
\begin{tabular}{c c c} \hline  & \multicolumn{2}{c}{**Participants (\(n\) = 216)**} \\ \hline  & \(n\) & Percent \\ \hline Women & 161 & 74.5 \\ Men & 55 & 25.5 \\ Ethnicity (\(n\) = 216) & & \\ Hispanic or Latino & 64 & 29.6 \\ Not Hispanic or Latino & 150 & 69.4 \\ Decline to state & 2 & 1.0 \\ Race (\(n\) = 216) & & \\ American Indian/Alaska Native & 3 & 1.4 \\ Asian & 24 & 11.1 \\ Native Hawaiian/Pacific Islander & 5 & 2.3 \\ Black/African American & 20 & 9.3 \\ White & 134 & 62.0 \\ Decline to state & 30 & 13.9 \\ \hline \end{tabular}
\end{table} 
Table 1: Sex, ethnicity, and race characteristics of the study participants. report the number of days during the past month they consumed a drink containing alcohol as well as the number of drinks they usually consumed when they drank. All participants were seated in a double-walled sound-treated room (Industrial Acoustics Company, Inc., North Aurora, IL, USA) for pure-tone air-conduction testing. Using supra-aural earphones (TDH-50P) connected to a clinical audiometer (GSI 61; Grason Stadler, Inc., Eden Prairie, MN, USA), binaural pure-tone air-conduction testing was completed from 0.25 through 8 kHz, including 3 and 6 kHz. All participants had normal hearing (\(\leq\)20 dB HL) based on pure-tone audiometry and normal middle ear function, confirmed with a type A tympanogram, binaurally, based on the tympanogram peak pressure range of +55 and \(-\)90 daPa and the peak acoustic admittance range of 0.3 and 1.8 mmho. The test ear was randomly determined for all subsequent research procedures. While the participant remained in the sound-treated room, a probe assembly was placed in the ear canal of participants and the participants were instructed to remain quiet during the procedure and there was no response needed. DPOAE stimuli were transmitted through ER 2 earphones (Etymotic Research Inc., Elk Grove Village, IL, USA) coupled to an ER 10B+ low noise DPOAE microphone (Etymotic Research Inc). DPOAE recordings were obtained between \(2f_{1}-f_{2}\) frequencies of 1 and 6 kHz using two stimulus tones swept in frequency at 8 sec/octave. The frequency ratio between the stimulus tones (\(f_{2}\)/\(f_{1}\);\(f_{2}\)\(>\)\(f_{1}\)) was fixed at 1.22 with stimulus levels fixed at L\({}_{1}\),L\({}_{2}\) = 55,40 dB SPL The use of these lower level stimuli has been shown to be sensitive to smaller noise-induced changes in otoacoustic emissions [25; 26].