Bring a Friend! Privately or Publicly?
研究卖家如何通过奖励知情消费者（影响者）来激励口碑传播，比较私下传播（按联系人付费）和公开传播（固定成本告知所有朋友）两种方式，发现网络密度对利润的影响因传播类型而异，最优策略是低成本激励高连接者公开传播，再为私下传播提供高额奖励。
We study the optimal referral strategy of a seller and its relationship with the type of communication channels among consumers. The seller faces a partially uninformed population of consumers, interconnected through a directed social network. In the network, the seller offers rewards to informed consumers (influencers) conditional on inducing purchases by uninformed consumers (influenced). Rewards are needed to bear a communication cost and to induce word of mouth (WOM) either privately (cost per contact) or publicly (fixed cost to inform all friends). From the seller’s viewpoint, eliciting Private WOM is more costly than eliciting Public WOM. We investigate (1) the incentives for the seller to move to a denser network, inducing either Private or Public WOM, and (2) the optimal mix between the two types of communication. A denser network is found to be always better not only for information diffusion but also for seller’s profits, as long as Private WOM is concerned. Differently, under Public WOM, the seller may prefer an environment with less competition between informed consumers, and the presence of highly connected influencers (hubs) is the main driver to make network density beneficial to profits. When the seller is able to discriminate between Private and Public WOM, the optimal strategy is to cheaply incentivize the more connected people to pass on the information publicly and then offer a high bonus for Private WOM. This paper was accepted by Juanjuan Zhang, marketing.