Dholakia, Utpal M. (2011년 6월 13일). “How Businesses Fare with Daily Deals: A Multi-Site Analysis of Groupon, Livingsocial, Opentable, Travelzoo, and BuyWithMe Promotions”. 《Social Science Research Network, Working Paper Series》. SSRN1863466.|url=이 없거나 비었음 (도움말)