An Agent-Based Model of Issue Alignment and Bipolarization Based on the Menu-Independent and Menu-Dependent Influences Model

Abstract

We present an opinion dynamics agent-based model (ABM) of issue alignment and bipolarization in two ideological dimensions: society and economy. The ABM formalizes and extends the menu-independent and-dependent influences (MIDI) model, a psychological theory of political attitude formation. The MIDI model posits that citizens naturally adopt social and economic attitudes that are congruent with a latent trait: their need for security and certainty (NSC). MIDI further posits that political discourse offers a menu of “internally consistent” ideologies, leading politically engaged individuals to adjust their economic attitudes for consistency. This ABM incorporates congruence bias into a peer influence mechanism: High-NSC agents gravitate toward socially conservative and economically leftist attitudes, while low-NSC agents gravitate toward socially liberal and economically rightist attitudes. A discursive influence mechanism leads agents to increase their “consistency” or decrease their “inconsistency” by adjusting their economic attitudes: Socially conservative agents move toward economic rightism, socially liberal agents toward economic leftism. The relative strengths of congruence bias and political engagement determine the emergent issue alignment. Counterintuitively, high congruence bias leads to bipolarization, even though the ABM lacks explicit polarizing forces like homophily, repulsion, or barriers to interaction. Finally, we show how the biased peer influence mechanism can model other latent-trait theories of issue alignment, such as the rigidity of the right hypothesis and the conflict of visions hypothesis.