I have an ACBC study with summed pricing and I've run an unconstrained estimation using piecewise coding for price.
It strengthened my belief that the utilities for the two lowest price ranges have positive slopes while for the rest of them they are negative on the average level (we ended up with quite a wide total range for summed prices, where the lowest prices might have made the respondent doubt the quality of the products shown which led to decline in their choices).
At the same time, I saw a reversal, even for average utility, for one of the higher prices, that can't be explained logically other than being caused by random noise and lack of choices.
So I would like to correct this issue by applying negative constraints for the higher prices while keeping lower prices unconstrained. However, it doesn't seem to be an option in the ACBC software (the constraint you choose would be applied to the whole attribute).
Could you please advise me a possible way to work this around?
Would an export to .cho and estimation in CBC/HB help?