The UK city of Rochdale is using machine learning to measure local wellbeing. Traditionally, if a local authority wanted to gauge public opinion it would commission an opinion poll, an expensive way of capturing a snapshot of sentiment on any one day. The Rochdale feelgood factor does away with interviews and harnesses the power of social media instead. Thousands of tweets sent from the town are studied on daily, with algorithms learning which words have a positive or negative context. Whereas the public don’t always respond entirely honestly to opinion pollsters, machine learning detects their true emotional state.