A spreadsheet comparing different BSA calculations on various patients-- and the resulting BSA-adjusted z-scores-- reveals negligible differences.
Can we compare z-scores from various references when the methods for calculating BSA are different? How?
If a given group of z-score equations are BSA adjusted, and a given patient has a different BSA depending on the BSA formula, how do you perform a comparison? Meaning, if equation A uses BSA formula x, and equation B uses BSA formula y, to what extent are differences in the z-scores due to differences in BSA?
Which then spawns these questions:
- What is a clinically important difference in BSA?
- a tenth of a meter2?
- a hundredth?
- a thousandth?!?
- How many significant digits are important when comparing z-scores?
I made this spreadsheet in an effort to examine some of these questions.
(the example z-score equation is from Kaiser et al., JCMR 2008.)
Looking over this data, I totally agree with Dallaire and Dahdah, JASE 2011, who noted:
There was virtually no difference when Z-score equations were derived from BSA estimated with different equations, and misclassification was rare.