Year	Percent
1998-01-01	56.875
1999-01-01	55.450
2000-01-01	54.825
2001-01-01	54.900
2002-01-01	55.250
2003-01-01	54.625
2004-01-01	54.175
2005-01-01	54.675
2006-01-01	55.050
2007-01-01	55.650
2008-01-01	55.925
2009-01-01	54.775
2010-01-01	54.175
2011-01-01	54.350
2012-01-01	54.525
2013-01-01	55.125
2014-01-01	55.700
2015-01-01	56.400
2016-01-01	57.550
2017-01-01	58.475