81 5 GRIX The GRIX consists of 14 questions and four subscales: xerostomia during day and night, and sticky saliva during day and night.22 The scores were transformed to a scale from 0 to 100, with a higher score indicating more problems regarding xerostomia or sticky saliva. Total xerostomia and sticky saliva were calculated by adding up the day and night scores to get a score from 0 to 200. In the present study, all subscales were used to explore the association between the PROs and salivary flow. Cronbach’s α of these scales ranges between 0.82 and 0.94, and test-retest reliability was between 0.63 and 0.67, indicating moderate correlations.22 Statistical analyses Data were tested for normality using a Shapiro-Wilk test. The associations between the WST, MAT, and salivary flow versus PROs were tested using Spearman’s rank correlation coefficient. The spearman correlation coefficient was categorized as very weak (0.0 to 0.1), weak (0.1 to 0.39), moderate (0.4 to 0.69), strong (0.7 to 0.89), and very strong (0.9 to 1.0).33 Scatterplots were created to visualize the MAT, WST, and salivary flow outcomes that had the highest correlation with one of the PROs. All analyses were performed using Statistical Package for the Social Sciences (SPSS) version 25 (Chicago, IL). A Bonferroni correction was used to account for the number of tests performed, in order to avoid a type Ι error.34 This correction was calculated by dividing the p-value by the number of tests performed. The corrected p-value was 0.05/12=0.004 for the MAT, 0.05/8=0.006 for the WST, and 0.05/8=0.006 for the salivary flow. A p-value ≤0.004 or 0.006 was considered statistically significant. Results The study cohort consisted of 142 patients out of the total NET-QUBIC cohort in the UMCU (n=154), of which 64 patients had repeated measurements for the MAT and WST at M0, M3, and M6. Twenty of these 142 patients had repeated measurements for the salivary flow measurements at M0, M3, and M6. Characteristics of patients can be found in Table 1a for MAT and WST measures, and Table 1b for salivary flow measures. In total, 285 assessments for the MAT and WST were carried out: 101 at M0, 92 at M3, and 92 at M6. For the salivary flow measurements, 167 assessments were carried out: 45 at M0, 65 and M3, and 57 at M6. All data except the MAT at M0 and M6 were not normally distributed. Boxplots displaying the outcomes of the objective measurements can be found in Figure 1. Regarding WST, there were missing data in 6 patients at M0 (5 patients because they were unable to drink the 100 mL, and 1 patient because of choking or coughing post swallow), in 12 patients at M3 (9 because they choked or coughed post swallow, and 3 because they were unable to
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