The medical definition of legal deafness is 66 to 85 decibels of hearing loss. On the scale of hearing loss degrees, this is considered severe. Anything over 85 decibels of hearing loss is considered profound. According to the U.S. Centers for Disease Control and Prevention, only those whose hearing impairment impedes their ability to comprehend speech and language are considered to have some level of deafness.
Those who are considered legally deaf have extreme difficulty in understanding speech, even with the assistance of hearing aids. At the profound level, hearing aids are not likely to contribute to any significant improvement in the ability to hear. It is estimated that as much as one-fifth of the American population had hearing loss severe enough that it impeded the ability to communicate. Although being legally deaf is associated with being medically classified as deaf, there are also social and psychological factors in considering the level of hearing loss. Cultural perception of the quality of one's hearing may lead to an individual being classified as deaf from a sociological perspective, even though the individual has not been diagnosed as clinically deaf. The same is true of individual psychology. It is possible for individuals to become convinced that they are deaf even though medical evidence suggests otherwise.