Year Percent 1999-01-01 42.575 2000-01-01 43.175 2001-01-01 43.125 2002-01-01 43.275 2003-01-01 44.300 2004-01-01 44.150 2005-01-01 44.200 2006-01-01 44.400 2007-01-01 44.100 2008-01-01 43.750 2009-01-01 43.050 2010-01-01 43.600 2011-01-01 43.675 2012-01-01 44.900 2013-01-01 45.375 2014-01-01 47.975 2015-01-01 49.450 2016-01-01 51.350 2017-01-01 52.075