Competition and collusion on the world coffee market
运用超级博弈模型分析垂直产品差异化对1993年咖啡生产国保留计划可持续性的影响，发现质量型合谋在高度差异化时更可持续，而全品类合谋中差异化对高低质量生产国的作弊激励有相反作用。
A supergame-theoretic model of collusion is used to analyse the impact of vertical product differentiation on the sustainability of the new retention scheme adopted by most coffee-producing countries in 1993. Taking arabica as the high quality variety and robusta as the low one, theoretical results suggest that: (i) quality-type collusions are more likely to be sustainable when products are highly differentiated while (ii) in the case of a collusion involving all countries (corresponding to the current arrangement on the world coffee market), product differentiation implies opposite effects on the incentive to cheat for low and high quality-producing countries. Product differentiation would deter robusta-producing countries from defecting but strengthen the incentive for arabica-producing countries to cheat. Moreover, it appears that the only way to enhance the sustainability of this kind of collusion is to allow arabica-producing countries to set the retention share. In addition, the negative impact of consumer heterogeneity on the sustainability of both kinds of collusion is highlighted.