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Subadditivity And The Unpacking Effect In Political Opinions, Renan Levine

Renan Levine

To explain subadditivity in judgments of probabilities, support theory (Tversky and Koehler 1994) emphasizes the increased availability of information about component events. This paper demonstrates that similar processes occur in responses to public opinion questions. When a broad description of a policy is “unpacked” into more specific component policies, support for the component policies exceeds support for the original, broad policy. This effect is especially strong when one or more of the unpacked policies make information available to the decision-maker that was not accessible when the broad description was provided. This behavior violates Luce’s (1959) axiom of independence of irrelevant …