The use of percentages and size-specific indices to normalize physiological data for variation in body size: wasted time, wasted effort?

Researchers commonly compute percentages or size-specific indices in an att empt to remove effects of body size from physiological data. Unfortunately, such ratios seldom eliminate the influence of body size on a physiological response and the ratios introduce major (but often unrecognized) problems with respect to statistical analysis and interpretation of the data. Indeed , these shortcomings of ratios frequently lead investigators to arrive at i ncorrect conclusions in otherwise flawless experiments. A superior alternat ive to using ratios combines graphical analysis and the analysis of covaria nce, which is a widely available statistical routine that uses least-square s regression to remove effects of body size from physiological data. Accord ingly, we counsel researchers to discontinue forming ratios in an attempt t o normalize physiological data for variation in body size and to adopt a re liable alternative. We also advise readers of scientific research not to pl ace great confidence in results of studies that use ratios for scaling. (C) 1999 Elsevier Science Inc. All rights reserved.