Prevalence refers to the estimated population of people who are living with SCD in a given time period. It is estimated that the prevalence of dehiscence of the bone overlying the superior canal is 0.5%–0.6%. An additional 1%–2% of individuals have been found to have an extremely thin (<0.1mm) layer of bone overlying the canal, which is also associated with vestibular or auditory symptoms. It should be noted, however, that not all persons with complete or partial dehiscence experience symptoms. The proportion that does is not well established (Carey, Minor & Nager, 2000; Crovettoa, et al., 2010).