MNL for how to set "no extra policy" choice

[AnnaChi]

Dear professor,
I am very new to DCE study.
I launched the pilot study and tried to analyze the pilot data using MNL in Stata to get the priors for Efficient Designs. And I got 22 questionnaires from pilot study.
In my design, I have three policy attributes , one policy effect attribute and one cost attribute. Because the research site don’t have any policy about green tide governing. So the choice C in DCE is not “status quo” but “no additional policy”,which means choice C have no level .I’d like to ask you how to set choice C as baseline in Stata or how to manage data in Excel. Should choice C be set as an empty item?
Anna

[Michiel Bliemer]

If an alternative has no specific attribute levels then it is probably an opt-out alternative. An opt-out alternative has either zero utility or has an alternative-specific constant. Stata uses long format I believe for estimating choice models, so the alternative would probably need to appear as a row in the data. I am not sure how to define opt-out alternatives in Stata, it may simply be a line with zeros, but please consult the Stata manual.

Michiel

[AnnaChi]

I got it, thank you for your advice!