Abstract: In this paper, the horizontal different assortment competition problem is studied with two circumstances: two retailers enter the market sequentially or simultaneously. Retailers decide their product assortment and consumer demand following the MNL (multinomial logit) model, based on which the profit function of retailers is depicted. Besides, a gradually substitute method for solving the best response is constructed, the method for solving the equilibrium in the two circumstances is given, and the results of the two circumstances are compared. The condition under which the order of retailers’ entry into the market does not affect the equilibrium result is given. The numerical results verify the effectiveness of the theoretical model. The results show that the gradual substitution method is an effective way for solving the best response and the equilibrium solution. If retailers enter the market sequentially, the equilibrium solution is unique, and the total number of products offered in the market must be not less than that when the retailers enter the market simultaneously. When the fixed utility of a product satisfies some specified conditions, the equilibrium result has nothing to do with the order of retailers’ entry into the market.

Key words: assortment decisions, first mover advantage, retailer competition, Nash equilibrium, horizontal differentiated products

摘要： 研究了零售商进入市场是否存在先后顺序情况下两个零售商的横向差异产品组合竞争问题。零售商分别决策产品组合，消费者需求服从MNL(Multinomial Logit)模型，在此基础上刻画了零售商的利润函数，通过构造逐步替代法求解最优反应，进一步给出了两种情况下求解均衡解的方法，并将结果加以对比，给出了零售商进入市场顺序不影响均衡结果的条件，数值分析验证了理论模型结论的有效性。结果表明：逐步替代法是求解最优反应和均衡解的有效方法；若零售商进入市场存在先后顺序则均衡解唯一，且市场提供的产品种类总数不小于零售商同时进入市场的情况；产品固定效用满足一定条件时均衡结果与零售商进入市场的顺序无关。

关键词: 产品组合决策, 先动优势, 零售商竞争, 纳会均衡, 横向差异产品