Year	Percent
1998-01-01	80.075
1999-01-01	79.900
2000-01-01	79.125
2001-01-01	78.575
2002-01-01	78.575
2003-01-01	77.950
2004-01-01	77.850
2005-01-01	78.350
2006-01-01	78.250
2007-01-01	78.125
2008-01-01	78.150
2009-01-01	78.500
2010-01-01	78.600
2011-01-01	78.675
2012-01-01	79.450
2013-01-01	80.475
2014-01-01	81.225
2015-01-01	81.375
2016-01-01	82.175
2017-01-01	82.875