Utility Sums for Alternative-Specific Design

Question

How do I address a colleagues concern that utility sums for product combinations resulting from conditional attributes in an alternative-specific design are artificially inflated due to summing the utilities of more attributes? Thanks!

Answer 1

I've never seen or heard such an argument against alternative-specific designs.  The classic bus-car-train-walk type examples from McFadden, Ben-Akiva, Louviere and others in the 1970s and 1980s featured alternatives with differing numbers of attributes.  There is no artificial inflation for an alternative because it has more attributes modifying it than another alternative with fewer.