Dear Statalist,

I have a date variable created the following way:

Code:
gen PartDat_gli = .
replace PartDat_gli = PartDat_NT2BLQ1 if copd_HUNT==1
replace PartDat_gli = PartDat_NT3BLQ1 if copd_HUNT==2
The original date variables are on this format:

Code:
              storage   display    value
variable name   type    format     label      variable label
----------------------------------------------------------------------------------------
PartDat_NT2BLQ1 long    %tdD_m_Y              Date and time participation HUNT2
                                                screening (Q1/M)
Generating the following variable:

Code:
              storage   display    value
variable name   type    format     label      variable label
----------------------------------------------------------------------------------------
PartDat_gli     float   %9.0g
It is the participation date for individuals with COPD who participated in either the first (NT2) or the second (NT3) cycle of a population study. I use the date variable to -stset- before -stcox-.
I now want to run a sensitivity analysis excluding the first 3 years of the follow-up time. How could I add 3 years for each participant to this date variable, taking into account the different participation dates? I tried to have a look at earlier threads in the forum, but I couldn't find a solution to my exact problem.

Best regards,
Sigrid Vikjord