Year Number 2004-01-01 11.7672 2005-01-01 14.3543 2006-01-01 16.1901 2007-01-01 17.5168 2008-01-01 18.2617 2009-01-01 21.4666 2010-01-01 29.6434 2011-01-01 31.8708 2012-01-01 37.5830 2013-01-01 29.5360 2014-01-01 32.1450 2015-01-01 33.5934