title: Classifying variables.
authors.affiliation: Department of Anaesthesiology, The University of Hong Kong, Hong Kong, HKSAR.
authors.forename: S W
authors.initials: SW
authors.lastname: Choi
authors.affiliation: Department of Anaesthesiology, Queen Mary Hospital, Hong Kong, HKSAR.
authors.forename: D M H
authors.initials: DM
authors.lastname: Lam
mesh_terms: D003627:Data Interpretation, Statistical; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007231:Infant, Newborn; D012016:Reference Values; D016008:Statistical Distributions; D014469:Umbilical Arteries / Q000378:metabolism; D014471:Umbilical Veins / Q000378:metabolism