MASS/LENGTH RESIDUALS: MEASURES OF BODY CONDITION OR GENERATORS OF SPURIOUS RESULTS?

In studies of animal ecology, it is fashionable to use the residuals from an ordinary least squares (OLS) linear regression of body mass against a linear measure of size (the body size indicator, BSI) as an index of body condition. These residual indices are used to study the relationship between condition and reproductive investment, survi- vorship, habitat use, and other parameters. I identify a series of key assumptions underlying the use of this method, each of which is likely to be violated in some or all studies. These