Stata intercooled for windows version 12

Continuous variables are presented as mean ± standard deviation (SD), while categorical variables as absolute frequency (relative frequency). Kruskal-Wallis, Pearson’s chi-square and Fisher’s exact tests were used to compare variables among COPD GOLD stages as appropriate. The unit of analysis was the patient. The survival function was calculated with Kaplan-Meier estimates for each GOLD stage and compared using log-rank test. Univariate and multivariate Cox regression analyses were performed to study the association between acute events and the following risk factors: age, gender, BMI, educational qualification, physical activity, smoking status, deprivation index, Charlson index and GOLD stages (Model 1). In a second model we replicated the analyses omitting the GOLD stage (Model 2). In a sensitivity analyses clinical variables such as PaO2 and FEV1 were considered instead of the GOLD stage. All P-values are based on 2-sided tests and P ≤ 0.05 were considered significant. Statistical analysis was performed using statistical package Stata Intercooled for Windows, version 12.0.