Year	Percent
1998-01-01	51.925
1999-01-01	52.675
2000-01-01	53.700
2001-01-01	54.800
2002-01-01	55.550
2003-01-01	56.100
2004-01-01	57.725
2005-01-01	57.575
2006-01-01	58.325
2007-01-01	58.575
2008-01-01	58.650
2009-01-01	57.350
2010-01-01	56.750
2011-01-01	56.800
2012-01-01	56.625
2013-01-01	55.525
2014-01-01	55.700
2015-01-01	56.275
2016-01-01	57.250
2017-01-01	57.975