Year Number 2008-01-01 21.9067 2009-01-01 20.8081 2010-01-01 21.6537 2011-01-01 23.7016 2012-01-01 31.4245 2013-01-01 24.0832 2014-01-01 23.2843 2015-01-01 25.1145 2016-01-01 26.9322