I am trying to replicate a study. It is an older study (2006) and in the study the respondents have to make a transport mode choice. The choice is binary, either public transport or car. In the original study the choice had car as a constant alternative, car, and a changing alternative public transport.
This is an alternative specific design. however I am wondering how I can hold the car constant (with different levels) and vary the PT component (bus, tram, train)? In the original design it had this constant car structure.
Does anyone have any suggestions?