In The Parable of Google Flu:
Traps in Big Data Analysis [PDF], published in Science, researchers try to understand why Google Flu (which uses search history to predict flu outbreaks) performed so well at first but has not done well since. One culprit: people don’t know what the flu is, so their search for “flu” doesn’t necessarily mean they have flu. More telling, though, is that Google can’t let outsiders see their data or replicate their findings, meaning that they can’t get the critical review that might help them spot problems before years of failure. (via Hacker News)