Variance inflation in sequential calculations of body surface area, plasma volume, and prostate-specific antigen mass
Article first published online: 5 AUG 2008
© 2008 VATTIKUTI UROLOGY INSTITUTE. JOURNAL COMPILATION © 2008 BJU INTERNATIONAL
Volume 102, Issue 11, pages 1573–1580, December 2008
How to Cite
Sivanandam, A., Siva, S., Bhandari, M. and Menon, M. (2008), Variance inflation in sequential calculations of body surface area, plasma volume, and prostate-specific antigen mass. BJU International, 102: 1573–1580. doi: 10.1111/j.1464-410X.2008.07883.x
- Issue published online: 21 NOV 2008
- Article first published online: 5 AUG 2008
- Accepted for publication 17 June 2008
- body surface area;
- plasma volume;
- PSA mass;
- variance inflation;
- robotic radical prostatectomy
To assess the magnitude of variability among 11 formulae for human body surface area (BSA) and then among eight for plasma volume (PV), as used to represent physiological indices for body metabolism, drug dosages and body fluid management, and to evaluate the potential cumulative effect of variance inflation with prostate-specific antigen (PSA) mass as an endpoint.
PATIENTS AND METHODS
In 3020 men undergoing robotic radical prostatectomy (RRP) at the Vattikuti Urology Institute between 2001 and 2008, the variation in BSA and PV formulae was calculated, as well as PSA mass, using analysis of variance (anova), Bland-Altman plots, linear regression, and correlation analyses.
For estimating BSA, anova indicated significant variance among the 11 formulae used (P < 0.001) with a between-groups variance of 5.45. Bland-Altman plots reported bias when the Dubois formula was compared to other BSA formulae. Furthermore the anova for PV, with BSA as a predictor, indicated significant variance among the eight formulae used (P < 0.001), with a mean between-group variance of 444.4 and a mean inflation factor of 81.5. Scatter plots between one PV formula (Boer) and others had a good linear fit. For PSA mass, anova indicated significant variance (P < 0.001) using PV as a predictor, with a mean between-group variance of 16 799.6 and a mean variance inflation factor of 37.8.
There is significant variation in the BSA calculated by commonly used formulae. This variation is carried over and further magnified in the sequential calculation of PV and PSA mass. Hence arbitrary selection of BSA and PV formulae is likely to affect inferences.