Year Number 2008-01-01 26.1499660656825 2009-01-01 29.2157307358783 2010-01-01 30.3877653012956 2011-01-01 27.2278234314215 2012-01-01 30.4343504486603 2013-01-01 26.2794916677199 2014-01-01 30.8200386325939 2015-01-01 29.6297103430843