As noted previously, the WGSS of questions was developed for adults and may not be capable of identifying children with learning or mental health related disabilities, leading to probable underestimation of the overall prevalence of child disability. Furthermore, the GBD calculations for disability prevalence are unusually derived from estimations of injury and disease prevalence, each of which is associated with an estimated distribution of disability severity. Consequently, the GBD estimates of disability prevalence are associated with three sources of major uncertainty.