Hi Everyone,

I am writing a thesis for my Honours year (Advanced Undergraduate Degree) and I am writing it on adolescent drinking levels with an excellent panel dataset. However, the panel data is split into two "cohorts" for example, it is set up as follows:

ID Wave Cohort X Y Z
33 1 K 3 5 7
55 1 B 4.3 6 1
33 2 K 23 123 213
55 2 B 312 32 1231
33 3 K 231 44 34
55 3 B 213 23 43

I want to know the effects on the different cohorts because they are different ages and have different effect levels. My (simplified) code is as follows:

sort cohort
by cohort: ologit alckid i.alcfreqp1 i.alcfreqp2 i.friendsalc, ro
by cohort: margins, dydx(alcfreqp1 alcfreqp2 friendsalc) post

However, I receive an error that the by command and the margins command may not be combined:

margins may not be combined with by

Does anyone have any suggestions for how I can run the margins command to find the margins by each separate cohort? I am struggling to find an alternative at this point.

Thanks in advance,

Jason