Accuracy of measurement, typical error of measurement, reliability, repeated measurement

Dual-energy X-ray absorptiometry (DXA) is rapidly becoming more accessible and popularas a technique to monitor body composition. The reliability of DXA has been examinedextensively using a number of different methodological approaches. This study sets up toinvestigate the accuracy of measuring the parameters of body composition (BC) by meansof the whole-body and the segmental DXA method analysis with the typical error of measurement(TEM) that allows for expressing the error in the units of measure. The researchwas implemented in a group of 63 participants, all of whom were university students.Thirty-eight males (22.6±2.9 years, average body mass 77.5±8.4 kg) and 25 females (21.4?2.0 years, average body mass 58.6?7.2 kg) were recruited. The measured parametersincluded body mass (BM), fat-free mass (FFM), body fat (BF), bone mineral content(BMC), bone mineral density (BMD). For the whole-body analysis, the determined TEMwas: BM at the level of 0.12 kg in females and 0.29 kg in males; BF 0.25kg and 0.44%females, 0.52 kg and 0.66% males; FFM 0.24 kg females and 0.42 kg males; BMC 0.02 kgfemales and males; BMD 0.01g/cm2 females and males. The TEM values in the segmentalanalysis were: BF within the range of 0.04-0.28 kg and 0.68-1.20% in females, 0.10-0.36kg and 0.72-1.94% in males; FFM 0.08-0.41 kg females and 0.17-0.86 males, BMC0.00-0.02 kg females and 0.01-0.02 kg males in relation to the body segment (upper limb,trunk, lower limb). The BMD value was at the level of 0.01-0.02g/cm2. The study resultsshowed high reliability in measuring body composition parameters using the DXA method.The whole-body analysis showed a higher accuracy of measurement than the segmental.Only the changes that are greater than the TEM, or the upper bound (95%) of the confidenceinterval of the measurement can be considered demonstrable when interpretingrepeated measurements.