Statistical Analysis
Descriptive statistics were calculated, and bivariate testing methods
included t and chi-squared tests. Overall survival (OS) was
calculated as time from diagnosis to either date of death due to any
cause or censoring at 5 years post-diagnosis. Subjects who were still
alive on December 31st, 2013 were censored on that
date. Hazard ratios (HRs) and 95% confidence intervals (CI) for the
independent effects of race on overall survival were estimated by Cox
proportional hazards regression models. Sequential adjustment sets were
used to examine the relative contribution of demographic, clinical and
SES variables to the racial survival disparity. Variables that were
missing >10% of observations were left out of the survival
analysis, which was determined as an a priori threshold. These
included rural/urban household designation (n=44 missing) and driving
distance to clinic where biopsy was performed (n=49 missing). All
variables were treated as categorical variables for the survival models.
The proportional hazards assumption was met for all covariates and there
was no evidence of multicollinearity on variance inflation factor
testing. STATA 16 (StataCorp, College Station, TX) was used for all
analyses.