bioimpedance anaylsys
BIA concepts
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regression equations

Bioimpedance analyzers use regression equations to compute amounts of fat-free mass, body cell mass, total body water and intracellular water.

What is a regression equation?
A regression equation is a mathematical formula that best predicts the relationship between two or more variables based on the analysis of data sampling. For example, the regression equation for total body water (TBW) is of the form:

   TBW = a * Ht2 / R + b * Weight + c * Age + d

The terms are Ht2 / R, Weight and Age. The weighing constants for the terms are a, b, c, and d.

Regression equations for bioimpedance analysis (BIA) are determined through research. For example, to determine the regression equation for TBW, a large number of subjects are analyzed for TBW using deuterium dilution or some other reference standard. Then, resistance, height, weight, gender, and age are supplied for each subject in the study. A computer generates an equation which best describes the relationship between TBW and resistance, height, weight, gender, and age. This process is called regression analysis.

How are regression equations used?
Regression equations are used to compute fat-free mass, body cell mass, total body water, and intracellular water. When the bioimpedance analyzer measures resistance and reactance, the results are passed to the analyzer's microprocessor to perform the calculations. The equations for FFM, BCM, TBW and ICW are encoded into the analyzer's internal software.

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