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)