Year	Percent
1998-01-01	55.900
1999-01-01	57.300
2000-01-01	58.900
2001-01-01	57.800
2002-01-01	57.550
2003-01-01	58.600
2004-01-01	61.025
2005-01-01	61.900
2006-01-01	62.350
2007-01-01	62.150
2008-01-01	61.925
2009-01-01	62.775
2010-01-01	65.800
2011-01-01	64.100
2012-01-01	65.100
2013-01-01	66.250
2014-01-01	66.175
2015-01-01	67.200
2016-01-01	68.750
2017-01-01	67.650