Hello. I am doing a dissertation on the epidemiology of Parkinson's disease in a district where I need to calculate the age-specific incidence rate but, I don't have data on the age group for that particular district. However, I do have data on the age group for my whole island.

My question is, can I use the data on the age group for my whole island to represent the age group for the particular district I am studying? (The district's population is about 30% of the island's population)