Results of impedance audiometry were analyzed in 1,133 consecutive patients with either normal or sensorineural audiograms. The static compliance of the normal middle ear varies uniquely with both the age and sex of the patient. In the normal ear, the threshold of the stapedial reflex to pure tones is normally distributed around a mean of approximately 85 dB hearing threshold level (ISO-64) with a standard deviation of 8 dB. In the ear with sensorineural hearing loss, the sensation level (SL) of the stapedial reflex declines in proportion to increasing hearing loss to a limiting (SL) of approximately 25 dB. The frequency of 4,000 hertz appears to be atypical. Absent reflexes at this frequency do not necessarily have pathological significance.
Jerger J, Jerger S, Mauldin L. Studies in Impedance AudiometryI. Normal and Sensorineural Ears. Arch Otolaryngol. 1972;96(6):513-523. doi:10.1001/archotol.1972.00770090791004