The “freemium” model for digital goods involves selling a base version of the product for free, and making premium product features available to users only on payment. The success of the model is predicated on the ability to profitably convert free users to paying ones. Price promotions (or “sales”) are often used in freemium to induce this conversion. However, the causal effect of exposing consumers to such inter-temporal price variation is unclear. While sales can generate beneficial short-run conversion, they may be harmful in the long-run if consumers inter-temporally substitute purchases to periods with low prices, or use them as signals of low product quality. These long-run concerns may be accentuated in freemium apps, where the base version is sold for free, so that sales form extreme price cuts on the overall product combination. We work with the seller of a free-to-play video game to randomize entering cohorts of users into treatment and control conditions in which promotions for in-game purchases are turned on or off. We observe complete user behavior for half a year, including purchases and consumption of in-game goods, which, in contrast to much of the extant literature, enables us to assess possible substitution over time in consumption directly. We find that conversion and revenue improve in the treatment group; and detect no evidence of harmful inter-temporal substitution or negative inferences about quality from exposure to price variation, suggesting that promotions are profitable. We conjecture that the zero price of the base product that makes its consumption virtually costless, combined with the complementarity between the base product and premium features can help explain this. To the extent that this holds across freemium contexts, the positive effects of promotions documented here may hold more generally.

数字商品的“免费增值”模式包括免费销售产品的基本版本，并仅在付费后向用户提供高级产品功能。该模式的成功取决于将免费用户转化为付费用户的能力。免费增值中经常使用价格促销（或“销售”）来诱导这种转化。然而，将消费者暴露于这种跨期价格变化的因果关系尚不清楚。虽然销售可以产生有益的短期转化，但从长远来看，如果消费者跨期将购买替代为低价时期，或将其用作产品质量低下的信号，则可能会有害。这些长期担忧可能会在免费增值应用程序中更加突出，其中基本版本是免费销售的，因此销售对整个产品组合形成了极大的降价。我们与免费视频游戏的卖家合作，将进入的用户群组随机化到开启或关闭游戏内购买促销的治疗和控制条件中。我们观察了半年的完整用户行为，包括游戏内商品的购买和消费，与现有的许多文献相比，这使我们能够直接评估随着时间的推移可能的消费替代。我们发现治疗组的转化率和收入都有所提高；并检测 使我们能够直接评估随着时间的推移可能的消费替代。我们发现治疗组的转化率和收入都有所提高；并检测 使我们能够直接评估随着时间的推移可能的消费替代。我们发现治疗组的转化率和收入都有所提高；并检测没有证据表明有害的跨期替代或因价格变化而对质量产生负面推论，这表明促销是有利可图的。我们推测，基本产品的零价格使得其消费几乎没有成本，再加上基本产品和高级功能之间的互补性，可以帮助解释这一点。如果这适用于免费增值环境，则此处记录的促销活动的积极影响可能更普遍。