This study was aimed to devise a theoretical formula for the mid-age of incidence (MAI) from the prevalence of age groups and to confirm its application. The formula was devised using the concept of lost years of health and then simulated. In the inhabitants’ survey, MAI was calculated from the prevalence of liver disease in the areas, and the main cause of disease was analyzed between those areas where MAI was lower than 2.5% of the distribution with significantly high prevalence (HL group) and those areas where MAI was higher than 2.5% of the distribution with significantly high prevalence (HU group). In the computer simulation, MAI was not much different or a little lower than the mid-age of occurrence. In addition, the sum of the incidence rates in the 1-year age groups approximately corresponded to the maximum prevalence within the age groups in the simulation. In the HL group, the main cause of liver disease was alcoholic liver injury; in the HU group, one cause was type C hepatitis, whereas for many others, it was advanced alcoholic liver injury. Thus, the HU and t HL groups were confirmed as active and quiescent areas, respectively. Investigating the cause or stage is considered to be useful in future studies.
Key words: Mid-age of incidence (MAI), Lost years of health, chronic disease, prevalence, age specific prevalence.
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