## 3 Results
A strong concordance between the two techniques was present for both sexes (Figure 2). Figure 1: Concordance plots for body fat percentage (%BF) measured by air-displacement plethysmography (AP) and bioelectrical impedance (BIA) in the study group (\(n=80\)), with the concordance correlation coefficient (CCC) (**A**) and Bland–Altman plot (**B**). The solid black line shows the bias (the mean of the differences) and the black dashed lines the 95% confidence interval (CI). The red solid lines represent the limits of agreement (bias \(\pm\) 1.96 SD of the differences), and the red dashed ones delimit their 95%CI. The linear regression equation between the differences and the means is given together with the \(p\)-value and the coefficient of determination (R\({}^{2}\)). Figure 2: Concordance plots for body fat percentage (%BF) measured by air-displacement plethysmography (AP) and bioelectrical impedance (BIA) for female (**A**) and male (**C**) subjects, with the concordance correlation coefficients (CCC). Bland–Altman plots for women (**B**) and men (**D**) show the bias as a solid black line, together with the 95% confidence, and the red dashed ones delimit their 95%CI. The linear regression equation between the differences and the means is given together with the \(p\)-value and the coefficient of determination (R\({}^{2}\)). When dividing subjects by BMI, BIA underestimated the %BF mainly in underweight and normal-weight persons. In these categories, the differences between the two techniques were 5.07 \(\pm\) 2.6% and 4.04 \(\pm\) 5.74%, respectively; these differences reached statistical significance. The CCC showed only a moderate concordance between the two body composition methods in these subjects, and the bias significantly increased with the %BF, as indicated by the Bland\(-\)Altman plot (Figure 3). In overweight and obese participants, representing approximately half of the study group, BIA underestimated the %BF compared to the AP with only 1.68 \(\pm\) 6.64% and 2.63 \(\pm\) 4.02% respectively, (neither was statistically significant with \(p>\) 0.05 in both situations). Central obesity was diagnosed according to the WHtR; in subjects with the WHtR \(<\) 0.5, the bias had a value of 2.97 \(\pm\) 6.21%. BIA underestimation was higher in those with central obesity (3.26 \(\pm\) 5.1%). In both groups, the differences between the two body composition techniques were statistically significant at \(p<\) 0.05 (Figure 4). Figure 3: Concordance plots with concordance correlation coefficients (CCC) for body fat percentage (%BF) in underweight and normal weight subjects (**A**) and in overweight and obese participants (**C**). Bland\(-\)Altman plots for subjects with BMI \(<\) 25 kg/m\({}^{2}\) (**B**) and with BMI \(\geq\) 25 kg/m\({}^{2}\) (**D**) depict the bias as a solid black line, with the 95% confidence interval (CI) as black dashed lines. The limits of agreement (bias \(\pm\) 1.96 SD of the differences) are shown as solid red lines, while their CIs are represented as red dashed lines. The linear regression equation between the difference and the means with the \(p\)-value and the coefficient of determination (R\({}^{2}\)) are shown.