Contingent valuation method

[Esther Waruingi]

I am using CVM to estimate mean WTP for a conservation program. WTP is elicited in both cash value and man labour days.
Is it mandatory that the two models should be estimated using similar variables or each model can have its set of explanatory variables?

[Hong Il Yoo]

It is not mandatory but my guess is that it will make interpretation of the results easier if you use the same set of regressors in both models.