Thank you so much!
I am working on PIAAC (OECD database).
It also propose the following answers:
6: Valid skip
7: Don't know
9: Not stated or inferred
So, I tried to do:
IF ( (J_Q06a + J_Q07a) < 3) parentsbirthplace = 1 .
IF ( (J_Q06a + J_Q07a) >= 3 <= 4)...