Hi All,
I am struggling with how to calculate mid-year population (as of 1st July) to calculate crude incidence for some prescription by GPs for each included year (i.e., 1997-2019) in a city. The denominator data contains the list of everyone who visited to GPs between 1997-2019 in that city, and multiple prescriptions possible for same individual. Data are available by date of visit to GP. Now, I need to calculate crude incidence of that prescription for each year. I am struggling to calculate mid-year (as of 1st July) population to use it as denominator as per the study protocol. May request to help me on how to calculate mid-year population?

Thank you in advance for your help.