Hi! I have a dataset that looks like this:   patient_id start_date     end_date 123           01Jan2016   15Apr2020 321           09Sep2018   17Nov2019 567            07Jul2017    09Jul2020 567            09Sep2020   10Dec2020   My study period is 01Jan2016-31Dec2020. I want to create a new variable called time that creates a flag if someone's study period included that particular month (ex. 1=Jan2016, 2=Feb2016, etc). So my data set would end up looking like this: patient_id start_date     end_date      time 123           01Jan2016   15Apr2020    1 123           01Jan2016   15Apr2020    2 123           01Jan2016   15Apr2020    3 123           01Jan2016   15Apr2020    4 etc   Any thoughts on how to do this? ... View more