Year	Percent
1998-01-01	52.025
1999-01-01	52.475
2000-01-01	52.875
2001-01-01	53.325
2002-01-01	53.725
2003-01-01	54.075
2004-01-01	55.000
2005-01-01	54.600
2006-01-01	54.775
2007-01-01	54.550
2008-01-01	55.050
2009-01-01	54.475
2010-01-01	54.300
2011-01-01	54.400
2012-01-01	55.550
2013-01-01	55.350
2014-01-01	55.775
2015-01-01	55.875
2016-01-01	56.600
2017-01-01	57.100