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.