Variable Competence and Collective Performance: Unanimity Versus Simple Majority Rule

Under the unanimity rule, a single voter may alter a decision that is unanimously accepted by all other voters. Under the simple majority rule, the impact of such a voter diminishes. This paper examines the marginal effect of competence on the collective performance—the likelihood of reaching a correct decision. It is shown that adding an incompetent voter to the group is inferior (superior) to giving up an existing competent voter, when the decision mechanism is the unanimity (simple majority) rule. The negative impact of an incompetent voter cannot (can) always be balanced by adding a competent one under the unanimity (simple majority) rule. Moreover, improving a single voter’s competence may have a greater effect on the collective performance under the simple majority rule relative to the unanimity rule.