We present simple and direct arguments to characterize strongly group strategy-proof social choice functions whose range is of cardinality two. The underlying society is of arbitrary cardinality, and agents can be indifferent among alternatives.

Recently, it has been shown that the characterizations of different classes of non-manipulable social choice functions with binary range can be reduced to a common functional form. In the present paper, we investigate the reasons why this happens. We show that all the classes considered share a...

Majority voting is considered an efficient information aggregation mechanism in committee decision-making. We examine if this holds in environments where voters first need to acquire information from sources of varied quality and cost. In such environments, efficiency may depend on free-riding...