Cumulative Incidence using 5 year estimates

Has anyone tried to calculate cumulative incidence using 5 year estimates by zip code? if so did you use one 5 year estimate multiplied by the number of years or the did you sum up the pop for all of the years? This paper has done it this way using  https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4864608/pdf/nihms784513.pdf (If you don't want to use the link, you can google "Multiple cluster analysis for the identification of high-risk census tracts for out-of-hospital cardiac arrest (OCHA) in Denver, Coloardo")

Thank you for any insight in advance.