Algorithms are running our society, and as the Cambridge Analytica story has revealed, we don't really know what they are up to. Our increasing reliance on technology and the internet has opened a window for mathematicians and data researchers to gaze through into our lives. Using the data they are constantly collecting about where we travel, where we shop, what we buy and what interests us, they can begin to predict our daily habits. But how reliable is this data? Without understanding what mathematics can and can't do, it is impossible to get a handle on how it is changing our lives. In this book, David Sumpter takes an algorithm-strewn journey to the dark side of mathematics. He investigates the equations that analyse us, influence us and will (maybe) become like us, answering questions such as: Who are Cambridge Analytica? And what are they doing with our data? How does Facebook build a 100-dimensional picture of your personality? Are Google algorithms racist and sexist? Why do election predictions fail so drastically? Are algorithms that are designed to find criminals making terrible mistakes? What does the future hold as we relinquish our decision-making to machines? Featuring interviews with those working at the cutting edge of algorithm research, including Alex Kogan from the Cambridge Analytica story, along with a healthy dose of mathematical self-experiment, Outnumbered will explain how mathematics and statistics work in the real world, and what we should and shouldn't worry about. A lot of people feel outnumbered by algorithms - don't be one of them.