Are choice model assumptions met?
If the IIA assumption does not hold, there are alternative methods for estimating choice models. To determine if alternative models are necessary, there are some useful tests to determine if IIA is violated.Since the ratio of choice probabilities between two modes is expected to remain unchanged relative to other choices, other choices could feasibly be added to the choice set and the original choice probability ratios should remain unchanged.A test proposed by Hausman and McFadden (1984) incorporates the use of a test conducted between the restricted choice set model (r), which is the model estimated without one of the choice alternatives, and a full model (f), estimated on the full set of alternatives.
