M. Andersson, J. Glass, и R. Simon. Social Indicators Research, 115 (3):
945-961(2014)First published online: January 19, 2013, http://dx.doi.org/10.1007/s11205-013-0244-8. (ISSP).
J. Cullis, J. Hudson, и P. Jones. Journal of Happiness Studies, 12 (2):
323-341(2011)First published online: March 3, 2010, http://dx.doi.org/10.1007/s10902-010-9190-1. (Eurobarometer).