Ratio of actual to predicted weight as an alternative to a power-type weight-height index (Benn index).

In 1971 Benn described a form of relative weight that can be calculated as the ratio of actual to predicted weight from the linear regression of weight on height in a population. He also showed how to compute the exponent for a power-type weight-height index that would be approximately equivalent to this relative weight. Benn did not, however, recommended that this "Benn index" be used instead of relative weight. The properties of these two weight-height functions were investigated in data on 10,606 white men and women aged 18-74 y examined in the 1976-1980 Second National Health and Nutrition Examination Survey (NHANES II). Compared with the power-type index, relative weight was preferable in that it was easier to compute with current software packages, was invariant at standard weight-for-height, and offered more flexibility. The limitations shared by both functions are discussed. Neither function should be used uncritically.