Considering people's wellbeing in making policy decisions is becoming more and more important, but it's only in recent years that governments have started to record the subjective satisfaction of the population. A team of researchers is looking to fill in the historical gap for national mood by analysing the text of old books published in the US, UK, Germany and Italy and computing a National Valence Index for each of these countries. Mariana Marasoiu spoke with lead author Thomas Hills about how it works... Like this podcast? Please help us by supporting the Naked Scientists