65 for both) and ratio (). The evoked responses from these stimuli occur at frequencies () mathematically related to the primary frequencies, with the two most prominent being (the "cubic" distortion tone, most commonly used for hearing screening), because they produce the most robust emission, and (the "quadratic" distortion tone, or simple difference tone). Clinical importance Otoacoustic emissions are clinically important because they are the basis of a simple, non-invasive test for cochlear hearing loss in newborn babies and in children or adults who are unable or unwilling to cooperate during conventional hearing tests. In addition, the OAEs are highly reliable making it suitable for diagnostic and screening applications. Many western countries now have national programmes for the universal hearing screening of newborn babies. Newborn hearing screening is state-mandated prior to hospital discharge in the United States. Periodic early childhood hearing screenings programs are also utilizing OAE technology. The Early Childhood Hearing Outreach Initiative at the National Center for Hearing Assessment and Management (NCHAM) at Utah State University has helped hundreds of Early Head Start programs across the United States implement OAE screening and follow-up practices in those early childhood educational settings. The primary screening tool is a test for the presence of a click-evoked OAE. Otoacoustic emissions also assist in differential diagnosis of cochlear and higher level hearing losses (e.g., auditory neuropathy). The relationships between otoacoustic emissions and tinnitus have been explored. Several studies suggest that in about 6% to 12% of normal-hearing persons with tinnitus and SOAEs, the SOAEs are at least partly responsible for the tinnitus. Studies have found that some subjects with tinnitus display oscillating or ringing EOAEs, and in these cases, it is hypothesized that the oscillating EOAEs and tinnitus are related to a common underlying pathology rather than the emissions being the source of the tinnitus. In conjunction with audiometric testing, OAE testing can be completed to determine changes in the responses. Studies have found that exposure to noise can cause a decline in OAE responses. OAEs are a measurement of the activity of outer hair cells in the cochlea, and noise-induced hearing loss occurs as a result of damage to the outer hair cells in the cochlea. Therefore, the damage or loss of some outer hair cells will likely show up on OAEs before showing up on the audiogram. Studies have shown that for some individuals with normal hearing that have been exposed