Is coffee bad for you?

People who drink more than 4 cups of coffee increase their chances of dying by 50%, it was reported recently. Given everyone’s chance of dying is already 100%, this seems a puzzle. What does the research really say, and how reliable are the findings? Plus, Ruth Alexander interviews economist and Expecting Better author Emily Oster, who used her statistical training to assess the evidence for herself on what effect coffee, alcohol and certain foods have on pregnant women. This programme was first broadcast on the BBC World Service.