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The audiometric records of 324 subjects with sensorineural hearing loss, presumed to be cochlear, were analyzed in order to develop norms for "disproportionate loss" in speech intelligibility. From the scatterplot relating PBmax to PTA2 (average of HTLs at 1,000, 2,000, and 4,000 Hz), and the scatterplot relating SSImax to PTA1 (average of HTLs at 500, 1,000, and 2,000 Hz), linear boundaries were constructed encompassing approximately 98% of observed values. A speech intelligibility score (PB or SSI) may be considered "disproportionately poor" if it falls below this empirically derived boundary.
Yellin et al. (Tue,) studied this question.