I have two subgroups of respondents: the ones who saw traffic-light labelling and the ones who did not. I am using likelihood ratio test to see if there is any difference in separating them into two groups or I should combine them into one. Here is my command codes:

clogit Response Price Drink1 Drink2 Drink3 if Label==0, group(UniqueID)
estimates store clogit1

clogit Response Price Drink1 Drink2 Drink3 if Label==1, group(UniqueID)
estimates store clogit2

clogithet Response Price d_Softdrink d_Juice25 d_FlavMilk d_Juice100 d_LowFatMilk, group(UniqueID) het(Label)
estimates store clogithet

lrtest (clogit1 clogit2) clogithet
The first two clogit commands worked totally fine while the clogithet command presented r(2000) error (no observations).

I used su and mdesc command to check but there is no missing data or string values in observations.

Could you please advise me on how to resolve this one?

Thank you.