Statistical Analysis
Demographic and clinical characteristics were compared between SES tiers using descriptive statistics. SES was compared with patient demographic, social, and clinical factors using Chi-square test for categorical variables and Kruskal-Wallis for continuous variables. For the outcomes of interest, unadjusted odds ratios were obtained from logistic regression models to determine independent risk factors. Variables for multivariate logistic regression were chosen based on backwards stepwise logistic regression for a p<0.05 as well as clinically relevant confounders determined by author consensus. The final multivariate model was adjusted for sex, age, race, residential area, distance to facility, SES, and insurance status. Collinearity was checked using variance inflation factor, and there was no evidence of covariance between independent variables in our final model. Significance was considered for p-values <0.05. All statistical analyses were performed using STATA SE 15.1 (Stata Corp., College Station, Texas).