Hello,

I'm having trouble when running a simple clogit command. My choice experiment is a labeled one with 6 choice cards per person, each card has 3 alternatives (one is status quo).
When running the command some of the attributes' values (they are set as dummy variables) are omitted due to collinearity. What can I do to avoid that?
The command is:

Code:
​​​​​​​cmclogit choice cost i.alt env_good env_mod env_exc size_both size_micro size_macro geo_eu geo_own waste_all waste_refund waste_ban waste_label cert_99 cert_75 cert_50 if status==3, iterate(30) basealternative(0)
Here is an example of the remarks generated when running the command:

note: cert_50 omitted because of collinearity
note: variable env_good has 2002 cases that are not alternative-specific; there is no within-case variability

I'd appreciate your help.
Thanks in advance!