Book excerpt: This book offers a critique of the popular claim that more data equals better health. In a study that redefines the public, academic, and policy debates around health, bodies, information and data, the authors consider the ways in which the phenomenon of self-diagnosis has created alternative worlds of knowledge and practices which are often at odds with professional medical advice. With a focus on data that concerns significant life changes, this book explores the potential challenges related to people's changing relationships with traditional health systems as access to, and control over, data continues to evolve.