Annals Academy of Medicine Letter to the Editor Dear Editor

Author: Aziz. Using
Language: English
Source: CiteSeerX
Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.551.4018
http://www.annals.edu.sg/pdf/37VolNo11Nov2008/V37N11p988.pdf
http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.551.4018
http://www.annals.edu.sg/pdf/37VolNo11Nov2008/V37N11p988.pdf
Identification number: ftciteseerx:oai:CiteSeerX.psu:10.1.1.551.4018

Summary

allometric scaling, the authors adjusted peak oxygen uptake (VO2max) for the confounding influence of body mass and found that mass exponents differed markedly for male and female athletes. I believe the mass exponent generated for the female athletes is the suspect. In the first place, Chia regressed VO2max on body mass (Fig. 1) and concluded that the 2 variables were non-linearly associated with each other. Without an inferential test to formally assess the difference between the linear and non-linear (loess) fits, I am uncomfortable in accepting this assertion. Yet, it is plausible that no association exists between the body mass and VO2max in Chia’s female athletes. A visual inspection of the scatterplot in Figure 1 tends to suggest that only a weak – and possibly, statistically insignificant – correlation exists between the 2 variables; hence, I believe the authors are obligated to report the zero-order correlation with the corresponding 95 % confidence interval (95 % CI). Furthermore, 2 arguments support my contention. First, the accentuated association (r = 0.71) between the ratio-scaled VO2max values and body mass (Fig. 2 with its correct caption found in Fig. 5) raises the possibility of a statistical artifact – that is, to the extent that little or no correlation exists between 2 variables, relating the part (i.e. body mass) to its whole (body-mass scaled VO2max) can yield a spurious (improved) correlation.2 Second and more importantly, the 95 % CI of Chia’s mass exponent (b = 0.24, 95 % CI, 0.10 to 0.54) was asymmetrical around the point estimate – and thus, misreported. If the upper bound of the 95 confidence limits reported by Chia were correct, the corresponding lower bound should be-0.10, and not 0.10. Accordingly, to the extent that the 95 % CI for the mass exponent contains 0, indicating that body mass should be scaled to the power of 0, no statistical association exists between body mass