I have a few questions regarding the interpretation of CBC HB part-worth utilities for my master thesis.

1) a negative average utility value DOES NOT say that the level is providing negative utility. Correct?

For example: An attribute has 4 levels. Utilities of level A and B have a negative sign. But that does not mean that A and B is disliked, right? We can not interpret the sign.

2) Can I report at which rate utility is increasing between levels? For example: Change from level A to B is 70. From B to C is 30. From C to D is 12. Can I state: Further increasing attribute X is still adding utility but the at a lower rate?

3)

Can I interpret the utility differences between levels?

For example, one level is regarded more negative than another since there is a utility difference of xy.

Suppose there is level A, B and C. Utility increase between A and B is very low / their utilities are similar. But utility increase from B to C is high. Can I then say that compared to level C, A & B are rather disliked? Also, can I say: utility increase is highest when increasing B to C?

4) Also, when I compare groups of people (e.g. demographics): Is it correct to say something like: Men drive more benefit out of level xy (∆U=7; p<0.05)? (For these comparisons I use the zero centered individual utilities and compare means via t-test)

The raw HB utilities are on the logit scale. That means that those utilities exponentiated are proportional to choice. Or, stated another way, the logit-scaled utilities are natural logs of probability-scaled scores. Yes, you can say that relative to C, A & B are less liked. And, on the logit scale, increase is less between A and B compared to either of those to C.

When comparing groups of people on a normalized scale (such as zero-centered utilities), you can say that one group of respondents prefer a level more relative to the other levels within the same attribute as another group.