## 2 Materials and Methods
### Statistical Analysis
#### 2.4.1 Criterion Validity  
To determine the degree of agreement and the presence of systematic error between the two instruments, the Lin's concordance correlation coefficient (CCC) was calculated. This statistic is expressed as \(\rho_{\mathrm{c}}\) = \(\rho\)\(\times\)\(C_{b}\), providing information on how close the pairing of the height data in both instruments is (\(\rho\), precision) and how close to ideality the relation is (\(C_{b}\), accuracy), where a straight-line \(x\) = \(y\) would be obtained [50]. The results obtained are classified as: \(\leq\) 0.9 (poor), 0.90-0.95 (moderate), 0.95-0.99 (substantial), and \(\geq\)0.99 (near perfect) [51]. [PERSON]'s bivariate correlation coefficient (\(r_{\mathrm{s}}\)) was also determined in this study as a means of conducting a correlational analysis. The use of this non-parametric equivalent to [PERSON]'s coefficient is justified due to the small sample size and the non-normal distribution of the sample [52]. For interpretation, the following criteria were used \(\leq\)0.1 (trivial), 0.10-0.29 (low), 0.30-0.49 (moderate), 0.50-0.69 (high), 0.70-0.89 (very high), and \(\geq\)0.90 (near perfect) [20; 53]. For the regression analysis, the Passing and Bablok regression [54] for non-parametric samples was used to test for the existence of a linear relationship between the paired data from both instruments. The relationship was established by the equation \(y=ax+b\), whereby the values of a variable \(y\) can be predicted as a function of another variable \(x\), where \(a\) represents the slope, in which its ideal value would be 1. This parameter provides information on the proportional differences between the two methods. On the other hand, \(b\) is the cut-off point with the \(x\)-axis (intercept) in which its ideal value, in this case, would be 0 and represents in a quantifiable way the systematic differences between the two devices. The standard error of estimate (SEE) was also calculated. Low values of SEE indicated that the points were closer to the regression line and, therefore, the magnitude of the estimated error was smaller. To study the existence of a systematic error, significant differences in the values of the _ADR jumping_ and the criterion instrument were calculated using a Wilcoxon test for paired samples and the effect size (ES) was determined as \(r=Z/\surd n\)[55]. The differences expressed as ES were interpreted according to [PERSON] et al. [56]: trivial (<0.19), small (0.2-0.59), moderate (0.6-1.19), large (1.2-1.99), very large (2.0-3.99), and huge (>4.0). Bland-Altman plots are used to assess the agreement between the height data of the two paired devices, allowing for the visualization of the differences between the two methods, and the extent to which the differences vary depending on the magnitude of the measurement. The limits of agreement (LoA) are defined as the interval within which the differences between the two methods of measurement are expected to fall with 95% confidence. LoA are calculated using the SD of the differences as LoA = \(\pm\)1.96 \(\times\) SD and represent the range within which 95% of the observed differences between the two methods of measurement are expected to fall. The maximum allowable differences were calculated from the coefficients of variation (CV) of each method according to the expression (CV\({}^{2}_{\mathrm{method1}}\) + CV\({}^{2}_{\mathrm{method2}}\))\({}^{1/2}\)[57], interpreting that the methods are not in disagreement if the 95% confidence limits of the upper LoA are below the maximum allowable difference and the lower LoA is above the maximum allowable difference [58]. The magnitude of the error was estimated by calculating the standard error of measurement (SEM); this statistic was calculated as SEM = \(S_{d}/\sqrt{2}\), where \(S_{d}\) is the standard deviation of the difference of the values [59]. This statistic provides information on the error in absolute terms from the analysis of the dispersion of the values around the true value [60].