Statistical Analysis
We summarize measures for the numerical and categorical variables. If
the distribution of the data was symmetric, we showed the variables as
means with standard deviation or, failing that, as medians with
interquartile range.
We applied the Student’s T-test to compare numerical variables with
symmetrical distributions. If the distributions were asymmetrical, we
used the Mann-Whitney U-test. We used the Kaplan-Meier method and the
log-rank test to compare survival functions. To contrast the study
hypothesis, we calculated the crude and adjusted Cox regression model or
the proportional hazards model. We calculated crude and adjusted Hazard
Ratio (HR), with a 95% confidence interval (CI). We entered the
confounding variables into the adjusted model if they had
p<0.05 in the crude analysis. Finally, we verified compliance
with the assumption of hazard proportionality in the Cox regression
model. All analyses were performed with the STATA statistical package
version 14.0.
Ethical approval: All procedures performed in studies involving
human participants were in accordance with the ethical standards of the
institutional and/or national research committee at which the studies
were conducted (Universidad Peruana de Ciencias Aplicadas; PI130-19)