Platform Economics in Modern Principles

Why is Facebook free? Why are credit cards less than free? Why do singles bars sometimes have women drink free nights but never men drink free nights? All of these questions are in the domain of platform economics. Platform economics is new. Tirole and Rochet practically invented the field with a seminal paper in 2003–and that paper was one of the reasons Tirole won the Nobel prize in 2014. Despite being new, platform economics deals with goods which are fundamental to the modern economy. Thus, Tyler and I thought that it was incumbent upon us to teach some of the intuition behind platform economics in Modern Principles of Economics. But students have enough new material to learn, so we set ourselves a challenge–explain the intuition of platform economics using principles that the students already know. Surprisingly, platform economics can be taught with just two principles: externalities and elasticities.

In our chapter on externalities we offer the students a puzzle. Why do some firms offer their workers free flu shots? The answer, as memorably illustrated in this video, is that the firm “internalizes the externality.” When one worker gets a flu shot, other workers at the firm are less likely to get sick. In principle, the workers could subsidize one another to achieve the efficient outcome but transactions costs makes that solution impractical (the Coase theorem). The firm, however, is already involved in transactions with all the workers and, as a result, it can subsidize flu shots and reap the benefits of workers taking fewer sick days. How much the firm should subsidize flu shots depends on the elasticity of flu shots with respect to the price and on the elasticity of sick days with respect to vaccinated workers.

Now what does this have to do with Facebook? Well think about seeing ads as a bit like getting a flu shot–seeing ads has a benefit to you but it’s also a bit of a pain so if you had a choice you might not watch that many ads. But advertisers want you to see ads–in other words, Facebook users who see ads create a positive externality for advertisers. The platform firm, Facebook, internalizes this externality and that means subsidizing ad-seeing by selling Facebook at a zero price to readers and instead charging advertisers. As we put it in Modern Principles:

Imagine that Facebook begins with a positive price for both readers and advertisers (PR>0 and PA>0). Readers, however, are likely to be sensitive to the price so a small decrease in price will cause a large increase in readers (very elastic demand). Thus, imagine that Facebook lowers the price to readers and thus increases the number of readers. With more readers, Facebook can charge its advertisers more, so PA increases. Indeed, if the demand for advertisers increases enough, it can even pay Facebook to lower the price to readers to zero! Thus, the key to Facebook’s decision is how many more readers it will get when it lowers the price (the reader elasticity), how much those readers are worth to advertisers (the externality of readers to advertisers) and how high can it increase the price to advertisers (the advertiser elasticity).

More in the textbook!


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