Year	Percent
1998-01-01	51.925
1999-01-01	52.075
2000-01-01	51.625
2001-01-01	51.225
2002-01-01	50.950
2003-01-01	50.800
2004-01-01	50.550
2005-01-01	50.675
2006-01-01	50.550
2007-01-01	49.775
2008-01-01	49.350
2009-01-01	49.525
2010-01-01	49.300
2011-01-01	49.475
2012-01-01	50.025
2013-01-01	50.900
2014-01-01	50.875
2015-01-01	51.250
2016-01-01	51.875
2017-01-01	52.275