Data Analysis
Statistical analyses were conducted using STATA MP-Parallel Edition Statistical Software, Version 18, College Station, TX: StataCorp LP. Ap -value of 0·05 was considered statistically significant. Descriptive statistics included mean and standard deviation for continuous-level data, median and interquartile range for ordinal data, and frequency and proportion for nominal data. Comparative analyses of demographic and clinical characteristics and study outcomes according to ABO blood type included Chi-Square Test of Homogeneity or Fisher’s Exact Test, Kruskall-Wallis H Test, and one-way Analysis of Variance (ANOVA). Relative risk of COVID-19 infection, disease severity, and disease outcomes (ICU admission, intubation, and mortality) according to ABO blood type was measured using risk ratio (RR), which was estimated using log-binomial regression.9 Crude risk ratios (cRR) were initially estimated. Afterwards, significant confounders were screened, analyzed, and controlled using a 10% change-in-estimate criterion10 to estimate the adjusted risk ratio (aRR).