Year Number 2007-01-01 6.3470 2008-01-01 7.2170 2009-01-01 7.8657 2010-01-01 8.7387 2011-01-01 7.5074 2012-01-01 12.4091 2013-01-01 13.9044 2014-01-01 15.0331 2015-01-01 16.8650 2016-01-01 21.4856 2017-01-01 23.8174