Hi all,

I am analysing a discrete choice experiment. I joined the project at a later stage, so I was not involved in the design of the experiment per se.

The core of the DCE was to see how different ways of framing information on energy efficiency affect the uptake of more efficient products. For this reason, three versions have been run: a control version plus two treatments which display energy efficiency in alternative ways. In the control group, the attribute energy efficiency can take on just 2 values (Energy Star yes, or Energy Star no). On the other hand, in the treatment groups energy efficiency can have 6 levels (1-6 based on monetary expenditures for electricity).

I want to run a mixed logit model pooling the three groups together. This is usually done by creating interactions between the attribute variable (EE) and treatment dummies (T1 and T2)
Code:
EE_T1 = EE * T1
EE_T2 = EE * T2
and including the attribute variable along with the interactions in the model
Code:
mixlogit choicer Price Stars OptOut, group(cluster_id) rand(Capacity Brand_n EE EE_T1 EE_T2) id(ID) cluster(ID) nrep(1000)
My problem is that energy efficiency does not have the same dimension in the three groups (it's a dummy for the control group, and a 1-6 categorical variable for the treatments), so I don't know how to create the EE variable to be interacted with the treatment dummies. Does anyone know how I can define the energy efficiency variable in this case in order to be able to run the pooled model?

Any suggestion will be greatly appreciated.

Thank you all in advance.

Stefano