Two professors at Harvard Business School have found evidence of racial discrimination on Airbnb, the site that lets people rent their extra space to guests for short term stays. The study, which was based on 3,500 listings in New York City, concludes that black hosts are earning 12 percent less than white hosts for similar properties. The study’s authors believe that emphasis exacerbates the problem of racial discrimination in online marketplaces. Discriminatory effects have been found in online marketplaces including Craigslist, where names commonly used by black people resulted in lower response rates, and the dating site OKCupid, where the site’s statistician writes that although race shouldn’t matter in messaging, it does.