I have a similar question. Using the Discover product for a simple CBC with a none option included, I am trying to determine, for each individual respondent, the aggregate utilities for specific product configurations. For example:
Utility(Attr1, Level1) + Utility(Attr2, Level 3) + Utility(Attr3, Level 1) = Total utility for this product, compared to total utilities for other product combinations
My questions are:
1) Should I be using raw or the zero centered utilities?
2) I understand that even the raw utilities that are output by Sawtooth are zero centered as a result of effects coding, but what I am struggling to understand is how this centering affects the ability to sum utilities from different attributes. Do I need to transform the raw utilities such that the lowest value one corresponds to a small or zero utility, for example? If so, how should I do this?
3) How do I treat the interpretation of a "negative" utility? I understand that a negative utility is not necessarily bad - it is just the lowest within that attribute if zero centered.