144 and history of alcohol intake (14 items), and alcohol dependence (7 items). The question ‘do you drink regularly’ was used to assess alcohol intake in the current study. Statistical Analyses Descriptive statistics were used to describe the study population. Differences between the total NET-QUBIC population and patients that filled in the SWAL-QOL were tested using ANOVA to assess differences in age, and chi-square tests were run to test for differences in sex, tumor site, tumor stage, primary treatment, alcohol consumption, smoking, comorbidity, and weight loss. Linear mixed models (LMM) were used to assess if demographic, clinical, and lifestyle factors influenced changes over time of the total score and all subscales of the SWAL-QOL. Akaike’s Information Criterion (AIC) was used to select the most appropriate covariance structure to fit the data.36 To account for within-patient correlations, a random patient factor was added, and a random intercept was used to account for the different entry levels of patients. The fixed-effect factors timing of assessment, tumor site, treatment modality, tumor stage based on TNM classification,34 sex, alcohol consumption, smoking, comorbidity, weight loss, HPV status, and age, as well as 2-way interactions of the factors treatment modality, tumor site, and tumor stage during the assessment period, were assessed. Timing of assessment consisted of 5 levels (M0, M3, M6, M12, M24), tumor site consisted of 3 levels (oropharynx, larynx or hypopharynx, oral cavity), treatment modality consisted of 4 levels (RT, CRT, surgery or CO2 laser, surgery with post-operative (C)RT), tumor stage consisted of 4 levels (I:Tis or T1N0M0, II:T2N0M0, III:T3N0M0 or T2N1M0 or T3N1M0, IV:T4aN0M0 or TanyN2M0 or T4bN0M0 or TanyN3M0),34 sex consisted of 2 levels (male, female), alcohol consumption consisted of 3 levels (drink regularly, seldom drink, drank in the past), smoking consisted of 3 levels (nonsmoker, former smoker, smoker), comorbidity consisted of 4 levels (none, mild, moderate, severe), weight loss consisted of 3 levels (no weight loss, 1-5 kg weight loss, >5 kg weight loss), HPV status consisted of 2 levels for oropharynx patients only (positive, negative), and age was defined as a continuous variable. The model included a stepwise backward selection of factors, in which factors that were not significant at a p<0.10 level were removed, beginning with the interactions. A hierarchical structure was maintained, meaning that if an interaction was included in the model, the main effects were also represented in the model. Risk factors were reported as estimated unstandardized regression coefficients with 95% confidence intervals (CI) and p-values. The coefficients of the significant covariates, together with the value of the intercept of the mixed model analysis, were combined into a formula for the estimated SWAL-QOL subscale. The intercept is the value of the estimated SWAL-QOL subscale in which all coefficients
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