Statistical Analysis
The quantitative data were described as the mean ± standard deviation
(SD), or as the median (min-max). A sample size calculation was
performed based on our observed results by using a one-sided McNemar’s
test. A sample size of 447 individuals, at least 49 in each arm, is
found to be sufficient to detect a clinically significant difference
between groups with 80% power and a 5% level of significance. The
qualitative data were described by the number of cases (proportion, %).
Patient characteristics were compared using the
χ2 test or Fisher’s exact test for categorical data
and the Mann Whitney U test for continuous data. Cox
proportional-hazards regression models were used to estimate the
association between QCB use and the composite endpoint of intubation or
death. Statistical significance was accepted when the probability (P)
value was <0.05 and changes were referred to as significant at
this P-value.