A Baseline ABM of Party Competition

This chapter specifies the “baseline” agent-based model of dynamic multiparty competition, which derives from an article published by (Laver 2005). This assumes that each voter has in mind some personal ideal “package” of policy positions and supports the political party that offers the policy package closest to this. The dynamic system at the heart of the model is as follows: voters support their “closest” party in this sense; party leaders adapt the policy packages they offer in light of the revealed pattern of voter support; voters reconsider which party they support in light of the revealed pattern of party policy packages; and this process continues forever. This recursive model describes policy-based party competition as a complex system, and the baseline model specifies three decision rules that party leaders may deploy when they choose party policy positions in such a setting. These rules are Sticker (always keep the same position), Aggregator (move policy to the centroid of the ideal policy positions of your current supporters), and Hunter (if your last policy move increased your support, make another move in the same direction; or else change heading and move in a different direction).