Replication data for: A Tournament of Party Decision

In the spirit of Axelrod’s famous series of tournaments for strategies in the repeat-play prisoner’s dilemma, we conducted a “tournament of party decision rules” in a dynamic agent-based spatial model of party competition. A call was issued for researchers to submit rules for selecting party positions in a two-dimensional policy space. Each submitted rule was pitted against all others in a suite of very long-running simulations in which all parties falling below a declared support threshold for two consecutive elections “died” and one new party was “born” each election at a random spatial location, using a rule randomly drawn from the set submitted. The policy-selection rule most successful at winning votes over the very long run was declared the “winner”. The most successful rule was identified unambiguously and combined a number of striking features. It satisficed rather than maximized in the short run; it was “parasitic” on choices made by other successful rules; and it was hard-wired not to attack other agents using the same rule, which it identified using a “secret handshake”. We followed up the tournament with a second suite of simulations in a more evolutionary setting in which the selection probability of a rule was a function of its “fitness”, measured in terms of the previous success of agents using the same rule. In this setting, the rule that won the original tournament pulled even further ahead of the competition. Treated as a discovery tool, tournament results raise a series of intriguing issues for those involved in the modeling of party competition.

本研究秉承阿克斯罗德著名的重复囚徒困境策略系列锦标赛的研究理念，在基于智能体（agent）的动态空间政党竞争模型中开展了一场“政党决策规则锦标赛”。我们面向研究者征集二维政策空间内的政党立场选择规则。所有提交的规则将在一系列长时程仿真中两两对抗；仿真设定中，连续两次选举支持率低于指定阈值的政党将“消亡”，每届选举都会从已提交的规则集中随机抽取一条规则，在随机空间位置生成一个新政党。长期来看在赢得选票方面表现最优的政策选择规则将被评为本次锦标赛的“获胜者”。本次锦标赛明确识别出了这条兼具诸多显著特征的最优规则：该规则在短期内遵循满意准则而非最优最大化原则；它会“寄生”于其他成功规则的决策行为；同时内置了不攻击使用同一规则的智能体的机制，后者通过“秘密握手”来识别同类。本研究在锦标赛结束后，又在更具演化特性的设定下开展了第二组仿真实验。在该实验中，规则的被选中概率取决于其“适应度”——即以使用该规则的智能体过往表现来衡量。在此设定下，首届锦标赛的获胜规则的竞争优势进一步扩大。若将本次锦标赛视作一种发现工具，其结果为政党竞争建模领域的研究者带来了一系列值得深入探讨的有趣议题。