Voting rules map collections of preference orderings over a set of candidates (one for each voter) to candidates. Now, in many contexts, we have to consider the case where either the voters’ preferences or the voting rule itself are incompletely specified. We consider here the family of voting rules consists of sequential majority comparisons, where the winner is computed from a series of majority comparisons along a binary tree. We address the computation of the winner of such voting rules, when the preferences and/or the binary tree are incompletely specified.