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While DEXA is the best practical method of determining body composition, its accuracy is not perfect. The best methods we have for determining the body composition of a living human are called "four component models" (4CM) which divide the body into water, [[Protein|protein]], mineral, and fat using radioactive isotopes to determine total body water and total body [[Potassium|potassium]]<ref name="Fuller-1992"/><ref name="Heymsfield-1990"/>. These methods are impractical, even in most clinical settings, but they can be used to evaluate DEXA and other techniques. A study of 152 people showed that DEXA corresponds well with the 4CM, but not perfectly<ref name="Van Der Ploeg-2003"/>. The graph below shows that DEXA tends to underestimate the body fat of leaner individuals. For DEXA values of 10, 20, and 30% body fat the 4CM showed 13.0, 21.6, and 30.3%, respectively. Overall, the DEXA scan had errors of up to −2.6 to 7.3% body fat, but the average error was only 1.6% (+/-0.8%).