A number of demographic, environmental, and medical characteristics have been linked to HL4 and therefore serve as potential confounders for the relationship between PDE-5i use and hearing impairment. Thus, in addition to sociodemographic characteristics (ie, age, race, household income), information pertaining to current smoking, the use of ototoxic medications, diabetes mellitus, cardiovascular disease, and job characteristics was selected from the MEPS-HC. Information regarding other potential confounders (eg, alcohol consumption) is not available in the MEPS, and therefore the confounding influence of such characteristics cannot be evaluated. Ototoxic medication use, including antibiotics, diuretics, salicylates, and quinine derivatives, was defined using the same information source used to define PDE-5i use. Information on acute and chronic medical conditions in the MEPS-HC is obtained via a number of mechanisms, including the report of a medical event (eg, hospital stay, medication purchase), whether the condition was responsible for 1 or more disability days, or if the condition was reported as “bothering” the person. For certain conditions (eg, diabetes mellitus, coronary heart disease) respondents are asked explicitly whether they were told by a physician or other health care provider that they have a specific condition. Medical conditions reported by respondents are coded by professional coders to International Classification of Diseases, Ninth Revision, Clinical Modification (ICD-9-CM) codes, although, to protect respondent confidentiality, nearly all codes are available only at the 3-digit level. This information was used to identify the presence of diabetes mellitus and cardiovascular disease, the latter including coronary heart disease, angina, myocardial infarction, or other heart conditions. Finally, the MEPS collects information related to current and former jobs, including industry and occupation. Industry and occupation codes are assigned by professional coders at the US Census Bureau based on verbatim descriptions provided by respondents during the survey interview. The detailed codes are collapsed into broader groups to ensure confidentiality. For the purposes of this analysis, individuals were classified as having ever worked in any of the following occupational categories: management/business/financial, professional, service, sales, office/administrative, farming/fishing/forestry, construction, production/transportation, or military.