Monetary variable in choice experiment

[Anna Beatriz Grigolon]

Dear Prof. Bierlaire

We are working on a choice experiment and are struggling with the inclusion of a monetary variable that will be dependent on improvements on a transportation system. However, the exact % increase in the fare relative to the improvement is not known. I have thus two questions:

1. How do make sure the alternative present a clear trade-off without a monetary variable? are there examples (references) that you suggest me to read?

2. How to include a monetary variable realistically in a choice experiment?

Thank you in advance 

Anna Grigolon