Year	Percent
1998-01-01	80.075
1999-01-01	80.675
2000-01-01	81.800
2001-01-01	82.300
2002-01-01	81.525
2003-01-01	80.925
2004-01-01	81.100
2005-01-01	80.700
2006-01-01	81.250
2007-01-01	80.925
2008-01-01	81.600
2009-01-01	79.675
2010-01-01	79.200
2011-01-01	77.800
2012-01-01	75.475
2013-01-01	74.575
2014-01-01	77.350
2015-01-01	78.825
2016-01-01	80.200
2017-01-01	82.550