Sample size and statistical methods
cancer, xerostomia
REGRESSION, CANCER, XEROSTOMIA
Assuming that sodium-hyaluronate mouthwash can cause a 20% reduction in the XQ scores when compared with the placebo, setting a bilateral 95% confidence interval and a study power of 80% in a crossover design, a minimum sample of 32 is required. Assuming a dropout rate of 20%, a sample size of 40 patients was required. The calculation was carried out using PASS2021 software. Such a high dropout rate was decided because of the particularly fragile nature of HNC patients and difficulty in predicting the course of cancer therapy in these patients.The clinical and demographic characteristics of the sample were described by applying descriptive statistical techniques. Qualitative variables are described using absolute and percentage frequencies, while quantitative variables are summarised either as mean and standard deviation (SD) when normally distributed or as median and interquartile range (IQR) when non-normally distributed. The intraclass correlation coefficient (ICC) test was used to determine the reliability between patients for each questionnaire at each time point. The ICC test was based on each question and the overall score. A coefficient major of 0.7 was considered reliable.The normality of quantitative variables was assessed using the Shapiro–Wilk test. Differences between groups for quantitative variables were assessed by the Mann–Whitney If any of the variables were associated with a reduction in xerostomia in univariate analysis, it was entered into a multivariate logistic regression model by inserting the therapy as a covariate and the XQ scores as outcome variables.Statistical significance was set at 