In the documentation for cmrologit, page 75 has:
In the Intro 6 of the cm doc, page 56 has:
I am having trouble reconciling these two statements. Or is there a difference between "incomplete," "evaluated but not given a rank," and missing?
cmrologit allows incomplete rankings and ties in the rankings as proposed by Allison and Christakis (1994). cmrologit permits rankings to be incomplete only "at the bottom"; namely, that the ranking of the least attractive alternatives for subjects may not be known—do not confuse this with the situation that a subject is indifferent between these alternatives.
cmrologit fits a choice model for rank-ordered alternatives for the case in which alternatives are not explicitly identified. That is, there is no variable specifying the alternatives. Alternatives are known only by their characteristics as given by a set of alternative-specific variables. All predictors must be alternative-specific variables. This model assumes IIA is true. It allows tied ranks. It also allows a subset of alternatives to be evaluated but not given a rank—equivalent to making them tied for the lowest possible rank.
