Year Percent 1998-01-01 38.900 1999-01-01 39.800 2000-01-01 42.925 2001-01-01 46.550 2002-01-01 48.475 2003-01-01 51.025 2004-01-01 51.425 2005-01-01 52.800 2006-01-01 54.800 2007-01-01 55.100 2008-01-01 57.075 2009-01-01 54.625 2010-01-01 55.600 2011-01-01 56.750 2012-01-01 56.625 2013-01-01 56.475 2014-01-01 56.775 2015-01-01 57.400 2016-01-01 59.800 2017-01-01 61.625