When the noise exceeds the signal: day-to-day variability in spirometry dominates LLN discordance

Robert A Rigby, Mikis D. Stasinopoulous, Achim Zeilis, Sanja Stanojevic, Gillian Heller, Fernanda de Bastiani, Thomas Kneib, Andreas Mayr, Reto Stauffer, and Nikolaus Umlauf contend that segmented linear regression (SLR) is inadequate for spirometry reference equations and over/under-diagnoses abnormality compared with Generalized Additive Models of Location, Scale, and Shape (GAMLSS). Using a refined NHANES 2007-2012 dataset (n=16,596), I reassessed calibration and the lower limit of normal (LLN) discordance with additional analyses. Out-of-sample root mean square error (RMSE) and correlations were essentially identical between approaches, and overall, below-LLN prevalence differed by