The double blind element of medical treatments is not always easy to reproduce in other fields, but the use of controlled trials is common in other areas. Technology companies often roll out two different versions of software online to subsets of users to see which gets the best response, as measured for example by click-through rates. This approach allows decisions to be data driven rather than based on judgement or experience. Tests on users may be ethically controversial, as Facebook found with experiments to its news feeds. And outcomes are not always desirable from the consumer’s point of view, for example when an option to turn down an offer is less visible on screen, even if few people want the offer. But effectiveness will likely have been demonstrated, at least for major websites.