Classification of Characteristics and Outcomes
Our exposures of interest were SES and insurance status. Insurance status was categorized as having private, public, or no insurance. The NCDB uses US Census Data to provide population-level estimates of median household income and educational status based on zip code of residence. The database adjusts for inflation and defines educational status as the percentage of adults in a zip code region that did not graduate from high school. Patients were grouped into three tiers of SES (highest, middle, and lowest) as determined by their geographical residence. The highest SES category reflected patients with an estimated median household income of ≥$48000 and living in a well-educated geographic region (<13% of adult residents not graduated from high school). The lowest category had an estimated median household income of < $48000 and lived in a less-educated geographic region (≥13% of adult residents not graduated from high school). The middle category was composed of discordant income and educational status (e.g. high income in a less-educated geographic region).
Our primary outcomes were two binary variables for the presence metastatic disease and increased tumor size (≥ 5 cm) at diagnosis. Metastatic disease was defined as patients with clinical or pathological metastases according to American Joint Committee on Cancer (AJCC) clinical and pathologic staging.24 Increased tumor size was defined as ≥ 5cm at the time of a patient’s diagnosis.