In 2008, media across the world announced with fanfare that Google engineers had found a method to predict the spread of the flu early on. The idea appeared sound. Users infected with the flu are likely to use Google’s search engine to diagnose their symptoms and look for remedies. These queries could instantly tell where the flu is spreading. To find the apt queries, engineers analyzed some 50 million search terms and calculated which of these were associated with the flu. Then they tested 450 million different algorithms to find the one that best matched with the data and came up with a secret algorithm that used 45 search terms (also kept secret). The algorithm was then used to predict flu-related doctor visits in each region on a daily and weekly basis.