Third, although it is difficult to compare the after-tax net hourly earnings of Uber’s driver-partners with that of taxi drivers, it appears that Uber driver-partners earn at least as much as taxi drivers and chauffeurs, and in many cases more than taxi drivers and chauffeurs. The prospect of higher compensation is likely part of the explanation for why the number of Uber driver-partners has grown at an exponential rate (along with lower entry barriers and flexibility). Another aspect of Uber that can influence the pay of driver-partners vis-à-vis taxi drivers is that customers rate their driver-partner when they take a trip with Uber, and driver-partners’ ratings are made available to potential customers. This leads Uber’s driver-partners to develop reputations, and to have an incentive to perform well to develop and maintain a good reputation. By contrast, taxi drivers typically are anonymous and customers are not aware of their reputations. Reputations matter in markets.26 Driver-partners are rewarded for having a good reputation, which could lead Uber’s driver-partners to earn more than taxi drivers. Furthermore, driver-partners who expect to do a good job and develop a strong reputation are more likely to be attracted to Uber than to traditional taxi service.27 Estimating the impact of driver-partners’ reputations on their earnings is an important topic for further research. The wage regressions that we present find little evidence of earnings differences by driver education, gender or race, but we do find a return to early experience using the Uber platform. Lastly, Uber’s growth rate has varied considerably across cities. Understanding why Uber grew more rapidly in some cities than others could provide insights into the likely future path of the on-demand sector. For example, if inefficient taxi regulations and restricted supply of taxi licenses contributed importantly to Uber’s rapid expansion, then demand for on-demand services may be slower outside of for-hire transportation services. 26 See, for example, Cabral and Hortaçsu (2010) for research on the relationship between sellers' ratings and sales on eBay, which, like Uber, is an online marketplace that uses a ratings system to build reputations for both sellers and buyers. 27 This sorting effect could partly explain why Uber’s driver-partners are more highly educated than traditional taxi drivers and chauffeurs. 32