Dear all,

I have a panel of 2 cross section. I estimate an individual fixed effects clogit nenjoy bmi i.sexofchild age, group(id)
and i get this from Stata "outcome does not vary in any group"

Please whats the cause and how can i fix this?

I then estimate clogit noenjoy bmi i.sexofchild age, group(age) and it works. However i don't know what to call this type of analysis which is grouped by age. Please i will like help with this.