The main assumptions of the method are: the distribution of disability by cause is entirely explained by diseases that are still present at the time of the survey and by the background; the cause-specific disability rates for each disease were proportionally equal in the time preceding the survey; individuals from the same age groups are exposed to the same background rate; the causes of disability (diseases and background) act as independent competing causes; and the start of the time at risk for disability is the same for all causes [9].