Data is everywhere, shedding light on all aspects of life. Retailers know what’s selling and who’s buying. Pollsters test opinions on everything from candidates to consumer goods. Doctors follow their patients’ vital signs. Social networks register the interactions of millions. Sensors measure the changing weather. And as athletes play, fans collect exhaustive statistics on their performance. If something can be measured, then in all likelihood a vast archive of data is already being compiled—and it is growing daily. Often, the data is unprocessed, waiting for someone to analyze it and discover new, valuable knowledge about the world.