Recent studies suggest that one common factor can be found in the "happiest" 10% of people: the strength of their social relationships. Psychological research also seems to show that, as people get older, they generally become happier, more content, and have a more positive outlook on the world.
Meanwhile, at the societal level, tools like The Happy Planet Index (see video below) measure the happiness of countries in relation to the amount of resources each one uses, while the Mappiness (see image) app beeps users once (or more) a day to ask how they're feeling, and a few basic things to control for: who they're with, where they are and what they're doing, and builds from this a barometer of societal mood.
