Five simple models of the implicit social process whereby a group combines individual preferences into a collective decision are investigated: plurality, majority, proportionality, equiprobability and highest expected value. For each model, an expression is developed which provides the probability that a group selects a given alternative, as a function of (i) group size, (ii) number of alternatives and (iii) the set of probabilities governing the likelihood with which a group member advocates each alternative. Predictions yielded by the probability expressions are used as the basis for a comparison of the models.