Statistical analysis
Descriptive statistics of sociodemographic and clinical data and quality-of-life questionnaires (EORTC and EuroQol-5d) and anxiety and depression scales (the HAD questionnaire) were measured as means and standard deviations and as frequencies and percentages for continuous variables and categorical data, respectively. To evaluate the influence of CT scanning, colonoscopy, chemotherapy and radiotherapy performed throughout the follow-up on the different outcomes, univariable generalized linear mixed models were used. Furthermore, multivariable generalized linear mixed models were used to evaluate the effect of those variables on mortality, complications, and recurrence at the next follow-up visit.
In the same way, univariable and multivariable generalized linear mixed models were used to evaluate the influence of the different quality indices in the health-related quality of life and anxiety and depression scales of the patients in the same follow-up period.
All the models were adjusted by sex, age, TNM stage, Charlson comorbidity index, tumor location (colon or rectum) and hospital. The variability explained by each model was determined by the coefficient of determination (R2).
All effects were considered significant at p<0.05. All statistical analyses were performed using SAS 9.4 (SAS Institute Inc., Cary, NC, USA).