Year Number 2005-01-01 16.6406 2006-01-01 17.2461 2007-01-01 19.4727 2008-01-01 20.7813 2009-01-01 19.7656 2010-01-01 19.2188 2011-01-01 19.5508 2012-01-01 19.1602 2013-01-01 19.4336 2014-01-01 19.8047 2015-01-01 17.9688 2016-01-01 17.0508 2017-01-01 16.6602