mass, if strict guidelines are adhered to. It is important to recognize that correlation is NOT a measure of accuracy or method agreement, BIA methods typically exhibit 2 standard deviation (2SD) limits of agreement with reference methods (e.g., DXA, MRI or 4C model) of around =/- 10%. Historical background The electrical properties of tissues have been described since 1872. These properties were further described for a wider range of frequencies on a larger range of tissues, including those that were damaged or undergoing change after death. In 1962, Thomasset conducted the original studies using electrical impedance measurements as an index of total body water (TBW), using two subcutaneously inserted needles. In 1969, Hoffer concluded that a whole-body impedance measurement could predict total body water. The equation (the squared value of height divided by impedance measurements of the right half of the body) showed a correlation coefficient of 0.92 with total body water. This equation, Hoffer proved, is known as the impedance index used in BIA. In 1983, Nyober validated the use of whole body electrical impedance to assess body composition. By the 1970s the foundations of BIA were established, including those that underpinned the relationships between the impedance and the body water content of the body. A variety of single-frequency BIA analyzers then became commercially available, such as RJL Systems and its first commercialized impedance meter. In the 1980s, Lukaski, Segal, and other researchers discovered that the use of a single frequency (50 kHz) in BIA assumed the human body to be a single cylinder, which created many technical limitations in BIA. The use of a single frequency was inaccurate for populations that did not have the standard body type. To improve the accuracy of BIA, researchers created empirical equations using empirical data (gender, age, ethnicity) to predict a user's body composition. In 1986, Lukaski published empirical equations using the impedance index, body weight, and reactance. In 1986, Kushner and Scholler published empirical equations using the impedance index, body weight, and gender. However, empirical equations were only useful in predicting the average population's body composition and was inaccurate for medical purposes for populations with diseases. In 1992, Kushner proposed the use of multiple frequencies to increase the accuracy of BIA devices to measure the human body as 5 different cylinders (right arm, left arm, torso, right leg, left leg) instead of one. The use of multiple frequencies would also distinguish