## 4 Discussion
Those results confirm the hypothesis that adjustments using the BIA measurements (resistance, reactance and/or impedance) and/or the initial BIA estimates (as TBW) can produce better results than using the BMC estimate provided by the equipment internal equation. At the same time, the results contradicted the findings of [PERSON] et al. [14], where the authors concluded that the BIA parameters were not able to produce better BMC estimates than the simple indices could (body mass and height, or age and height). However, such conclusions were drawn based on models generated with potentially highly correlated variables such as body mass, height, and age without presenting the correlation values, thus hindering further analysis to avoid the risk of overfitting in those models. The improvement on the BIA BMC estimates using the BIA measurements and the subjects' physical and biological characteristics (as HIV infection parameters) found in this study can be related to the variation of the FFM hydration over the years, decreasing from birth (when approximately 80.6% of the FFM is composed of water), reaching 75.1% and 76.9% at 10 years of age (for boys and for girls, respectively) [28]. Additionally, specific to the population that was studied, the chronic exposure to HIV ART may result in tissue dehydration [7; 12]. Previous studies that investigated the BIA's usability, suggested that multi frequency equipment can produce better BMC estimates when compared to a half-body analysis with single frequency (50 kHz) equipment [7; 9; 12]. Based on that, the third set of models was generated with the purpose of investigating whether the BIA total body analysis using multi frequency equipment was able to produce a better BMC estimate than the half body analysis using single frequency (50 kHz) equipment could. The similar results obtained by models 3B and 4B compared to those of models 2, 3A and 4A did not support this hypothesis. However, based on the assumption that a total body analysis using multi frequency equipment does not produce better results than a half analysis does using single frequency (50 kHz) equipment, we need to consider that the results from this study were obtained from a simulation and not directly from single frequency equipment. Models 3B and 4B were generated as options to the researchers who wanted to investigate the BMC estimate by the BIA with a half-body analysis using single frequency (50 kHz) equipment. The interpretation and applicability of the results from this study should consider the following limitations: (a) the use of only one reference method, (b) the construction of half-body equations using BIAsMF, and (c) the lack of access to the equipment equations to the measure the mineral content and estimate the BMC. The use of multiple reference methods can be an useful strategy, considering that the methods have distinct accuracy and limitations to evaluate the body composition components [9; 12; 29]. The selection of DXA as a reference method was based on the credibility of the technic as the standard reference method to evaluate the BMC [7; 8; 12] and its frequent usage in BIA validation studies [9]. In addition, BIA BIAsMF and tetrapolar equipment produce total and half-body estimates, respectively [12]. For this study, BIAsMF was used to provide results simulating single-frequency tetrapolar equipment. This simulation can result in future interpretation errors, and these should be investigated in future studies. BIA multifrequency equipment estimates the mineral content, and it usually provide this value as the BMC, however, the manufacture did not provide access to the equipment equations to researchers, limiting the knowledge about which independents variables already were used to estimate the mineral and BMC, and consequently, this could have resulted in the overfitting of the models.