Hi somebody there. I am new to start and I am trying to regress panel data from a huge cohort that followed up 10000k+ people for 10+years. My data is in the long panel and i am trying to regress it. Patients were followed up at different time points and as such some patients had many evaluations in a year (some with more than 2 evaluations in one month). When i try to use xtreg, STATA returns an error message "repeated time values within panel". I guess this is because some patients had more than one evaluation in a year. Can i use date of evaluation as as the time variable?

I am clueless on what is happening.

Thanks