Hedonometer.org is an instrument that measures the happiness of large populations in real time. The hedonometer is based on people’s online expressions, capitalizing on data-rich social media, and measures how people present themselves to the outside world.
Philipp Heim, Jürgen Ziegler, and Steffen Lohmann. Proceedings of the International Workshop on Interacting with Multimedia Content in the Social Semantic Web (IMC-SSW 2008), volume 417 of CEUR Workshop Proceedings, page 49--58. Aachen, (2008)