The Bone-anchored hearing device (BAHD) and the Contralateral Routing of Signals (CROS) hearing aid are two intervention methods designed to improve hearing in people who have significant hearing loss in one ear only. The BAHD is a surgically implanted device which also includes an external processor; sounds from the poor ear are transmitted to the good ear through skull vibrations. The CROS does not involve surgery; instead a hearing aid is fitted behind each ear, and the sounds on the side of the poor ear are wirelessly transmitted to the good ear.