I do not have access to ISO documents 389-1 or 389-2 which may provide the answers or the references needed to answer this question. I’m hoping one of you may know the answer or direct me to an appropriate reference.
Back in the early days (Beasley, 1935, Dadson and King, 1952 and Glorig, 1954, 1955) of developing norms for hearing threshold it was shown that norms varied based on whether the data were collected using “survey” methods (large N but less rigorous screening and less precise threshold measurement methods) or a “lab-based” (generally smaller N but more stringent exclusion and more precise method for threshold assessment) to derive threshold (See Glorig, 1956).
My question is: what method was used to derive the current norms? It would be most helpful if someone could provide the reference(s) for the studies used to determine audiometric zero in the current ISO standards.