Calculation of reference values for lung function tests.

The powerful computers that are now available enable calculation of reference values by endless permutations of regression models that are not always biologically meaningful. The aim of this study was to test the ability of simple regression models to describe data that has been collected for calculation of reference values. Healthy non-smoking females (n = 74) and males (n = 51) were studied with 22 commonly used lung function tests. If the data were logarithmically transformed, there was a satisfactory reduction of residual variation and the assumption of normality was fulfilled. Furthermore, the difference between males and females could be described by a binary sex-variable that is independent of interactions with other variables such as age, height and weight. Logarithmic transformation of lung function measurements followed by linear regression is recommended as a simple standard method for calculation of reference values.