Why Do Payment Card Networks Charge Proportional Fees?
解释了支付卡网络为何按交易金额比例收费而非固定每笔费用，发现当网络和商家都有市场势力时，比例费用能带来更高利润，但商家利润更低，消费者效用和社会福利更高。
This paper explains why payment card networks charge fees that are proportional to the transaction values instead of charging fixed per-transaction fees. We show that, when card networks and merchants both have market power, card networks earn higher profits by charging proportional fees. It is also shown that competition among merchants reduces card networks' gains from using proportional fees relative to fixed per-transaction fees. Merchants are found to earn lower profits under proportional fees, whereas consumer utility and social welfare are higher. Our welfare results are then evaluated with respect to the current regulatory policy debates.