Statistical analyses

All statistical analyses were performed in STATA, version 13.0 (Stata Corporation, College Station, TX). For bivariate analysis, the chi-square test and t-test were used for nominal and continuous variables respectively. Logistic regression was used in adjusted analyses and results are presented as adjusted β-estimates and 95% confidence intervals or adjusted least squares mean estimates and standard errors. The data was square root transformed for statistical analysis as appropriate to normalize distributions.