Hearing-impaired listeners vary more than normal hearers in quiet threshold, complicating averaging

Evidence

Simplified psychoacoustical tuning curves have been measured for normally hearing subjects using the method described above. Because threshold in quiet varies somewhat for normally hearing subjects and varies even more for hearing-impaired listeners, a meaningful averaging procedure has to be introduced. — Professor Dr.-Ing. Hugo Fastl, Professor Dr.-Ing. Eberhard, Psychoacoustics- Facts and Models, 1883