Exposure, Outcome, and Covariates
SEER variables for insurance and age were combined to create a new 3-level categorical variable of insurance status, defined as: 1) Insured; 2) Medicaid; and 3) Uninsured. The Insured category comprised patients within the following levels of the SEER insurance variables: 1) Private insurance: fee-for-service; 2) Private Insurance: Managed care, HMO or PPO, TRICARE; 3) Medicare- Administered through a Managed Care plan; 4) Medicare with private supplement; 5) Medicare with supplement, NOS and Military; and 6) Insured, No Specifics. The Medicaid category included patients within the following levels of the SEER insurance and age variables: 1) Indian/Public Health Service; 2) Medicaid; 3) Medicaid- Administered through a Managed Care plan; 4) Medicare with Medicaid eligibility; and 5) age ≥ 65 years or greater and are “uninsured” or “unknown”. The Uninsured category was comprised of: 1) Not insured; 2) Not insured, self-pay; and age <65 years. Our outcome variable, treatment type, was dichotomized as definitive (primary surgery with or without adjuvant treatment) and non-definitive treatment (radiotherapy ± chemotherapy without primary surgery). Data on clinically relevant covariates was also extracted, including age at diagnosis (categorized as 19-29, 30-59, 60-79, 80+ years), sex, year of diagnosis, marital status (married, unmarried, separated, divorced, widowed, unknown), race (defined as White; Black; American Indian, Native American, or Hawaiian; Chinese; Japanese; Filipino; Asian Indian or Pakistani; other; unknown), and oral cavity subsite. Year of diagnosis was categorized as pre-ACA (2007-2013) and post-ACA (2014-2016).