How to calculate follow_up years in longitudinal dataset

[nwang5]

I tried to get the follow_up year of my dataset. This survey was conducted every two years. Is there any code that works for this? Thanks!

                                     Obs    ID    lle9    lle10   lle11   lle12   lle13   lle14      expect_results

                                     1      1      .       0       0       0       1       .                   6
                                     2      2      0       0       0       .       .       0                   10
                                     3      3      0       .       .       0       .       .                   6
                                     4      4      .       0       1       1       1       1                   8
                                     5      5      .       .       0       .       1       4                   6
                                     6      6      0       .       1       .       .       2                   10

[ballardw]

You have to walk us through the logic of how you get 6 or 10 or 8 or whatever. Probably in lots of details.

Especially since I see nothing there that is obviously a "year" to calculate what a "follow_up" year may be.

[FreelanceReinh · Accepted solution]

Hello @nwang5,

Try this:

data want;
set have;
if n(of lle:) then
   n_FU_years=2*(7-whichn(coalesce(of lle14-lle9), of lle14-lle9)
                  -whichn(coalesce(of lle9-lle14), of lle9-lle14));
run;

If it doesn't work for your real data, then I agree with ballardw that we might need to go through lots of details.

[nwang5]

It works! Thank you so much!