使用开始和结束日期以及疾病发生日期计算 R 中的疾病发生率

Question

I have cohort study data with start and end dates for each patient. I would like to calculate the incidence of a disease in each year and each month from the first of January 2014 till the end of August 2021. How can I calculate person-months and person-years using the start and end date for each patient so I can get the incidence using the equation: number of new cases/ total population during time frame?

This is how my data currently looks like:

patid	start_date	end_date	disease	disease_date
1	01/03/1993	31/08/2021	yes	15/11/2017
2	24/03/2000	31/08/2021	no	NA
3	01/03/2020	23/08/2021	yes	15/08/2020
4	24/03/2016	01/08/2019	no	NA
5	24/03/2001	17/08/2020	no	NA
6	01/03/1999	04/08/2014	yes	01/01/2014
7	01/03/2016	31/08/2018	yes	18/03/2017

Answer 1

Please try the below code where i used the formula number of events/(end_date-start_date+1/365.25)*100

df2 <- df %>% mutate(start_date=as.Date(start_date,'%d/%m/%Y'), 
end_date=as.Date(end_date,'%d/%m/%Y'), disease_date=as.Date(disease_date,'%d/%m/%Y'), 
                     person_year=as.numeric(end_date-start_date+1/365.25)
                     ) %>% group_by(patid) %>% mutate(n=n(),
                                                      per_year2=(n/person_year)*100)