How do companies and governments go about influencing our behaviour? It's all about incentives, nudges and knowing what motivates us. But doesn't this all smack of manipulation? Many would argue changing someone's behaviour starts with knowing everything about them. Colm O'Regan and the BBC's technology correspondent, Rory Cellan-Jones, investigate the "quantified self", where you measure everything from the number of hours you sleep to the number of calories you eat in a day. But can a set of facts and figures really give you the whole picture? Are we being blinded by data and numbers, and losing sight of some greater truth in the process? Manuela Saragosa is joined by three people who know a lot about how to change behaviour: Jo Arden, strategy director at the marketing consultancy, 23Red; Steve Martin, Director of Influence at Work; and Josh Kaufman, author and business advisor.