Statistical software version

Various survival curves were calculated according to the Kaplan–Meier method. Overall survival (OS) was defined as the date from the first day of curative treatment to death of any cause or the date of the last follow-up visit. Progression-free survival (PFS) was defined as the time from the first day of curative treatment to the time of disease progression or death. Local failure-free survival (LFFS), regional failure-free survival (RFFS), and distant metastasis failure-free survival (DMFFS) were calculated from the first day of curative treatment until the day of the primary, neck, or distant relapse or the date of the last follow-up visit. Survival differences between different subgroups were analyzed using the log-rank test. Patient characteristics and other variables were compared, as follows. The Mann–Whitney test was used for age, the continuous variable, of the two groups. The chi-square test was used for categorical or ordinal variables. Fisher’s exact test was used when a small sample size existed. All statistical tests were two-sided, and a p-value of less than 0.05 is considered statistically significant. Analyses were performed by using MedCalc Statistical Software version 20.014 (MedCalc Software Ltd, Ostend, Belgium).

All statistical analyses were performed using MedCalc Statistical Software version 18.11.6 (MedCalc Software, Ostend, Belgium). Data were expressed as a percentage (for the categorized variable), median and standard deviation (for continuous variables). We considered p values below 0.05 to be statistically significant. The analysis of survival was carried out using the Kaplan–Meier estimation method with calculation of the hazard ratio (HR) and 95% confidence interval (CI).

Statistical significance was calculated using a one-way ANOVA with a Tukey–Kramer post hoc test for multiple comparisons (MedCalc^® Statistical Software version 22.009, Ostend, Belgium). Data are presented as group mean (M) ± standard error of the mean (SEM). A p value of less than <0.05 was considered statistically significant for all comparisons.

Data were presented as mean ± standard deviation (SD) for continuous variables and as number (percentages) for categorical variables. The various strain parameters measured in this study were compared to those of normal healthy patients previously published in literature including two meta-analyses with pooled data from > 2000 patients each for both the 2D and 3D global strain measurements [23 (link)–25 (link)]. Agreement between parameters in 2D and 3D were assessed using the concordance correlation coefficient (CCC) with 95% confidence interval (CI). Associations between two continuous variables were measured using the Pearson (r) or Spearman correlation (ρ) coefficient. Variability between the two sets of measurements was reported as the mean difference ± SD and the ICC with 95% CI. Means for 2D and 3D GLS, GCS, and GRS were compared with the one-sample t-test using reference values obtained from two large meta-analyses [23 (link), 24 (link)]. All other means were compared with the two-sample t-test. Data were analyzed with JMP 10.0 software (SAS Institute Inc., Cary, North Carolina) and MedCalc statistical software, version 11.4.1.0 (MedCalc Software, Ostend, Belgium). A P value < 0.05 was considered statistically significant.

In this work, we conducted all statistical analysis using the Pearson correlation coefficient and the Student t-test using MedCalc Statistical Software version 13.0.6 (MedCalc Software bvba, Ostend, Belgium; http://www.medcalc.org; 2014) [68 (link)].