*2.6. Data Analysis*

Statistical analysis was performed using the SPSS software for Windows (version 22, IBM Corp., Armonk, NY, USA). Firstly, the Kolmogorov–Smirnov test was utilized in order to assess normality distribution. Secondly, the descriptive analysis for the total sample was performed. Finally, a comparative analysis for both groups was developed. The mean, standard deviation (SD) and Student´s *t*-test for independent samples were employed for the parametric data. For the non-parametric data, median, interquartile range (IR) and Mann–Whitney *U* test were realized. Moreover, Levene´s test was performed to assess the equality of variances. The Fisher exact test was used to compare differences between sex and group. In addition, bar graphs completed with the 95 confidence interval (CI) error bars were added in order to illustrate the differences between both groups. For all statistical tests, an α error of 0.05 (95% CI) and a desired power of 80% (β error of 0.2) were employed.

In addition, a multivariate analysis was carried out using a linear regression (stepwise selection method; *Pin* = 0.05; *Pout* = 0.10) in order to predict the influence of the descriptive data and group (presence of Achilles tendinopathy) on the statistically significant outcome measurements (showed in the prior described analyses). The dependent variables were CFP thickness and PF thickness at calcaneus insertion. The independent variables were group, sex, weight, height, BMI and age.
