Year	Percent
1998-01-01	78.725
1999-01-01	80.325
2000-01-01	80.850
2001-01-01	81.425
2002-01-01	81.525
2003-01-01	81.125
2004-01-01	81.025
2005-01-01	81.700
2006-01-01	82.450
2007-01-01	83.350
2008-01-01	84.300
2009-01-01	82.400
2010-01-01	81.550
2011-01-01	82.275
2012-01-01	81.975
2013-01-01	81.025
2014-01-01	80.475
2015-01-01	79.950
2016-01-01	79.925
2017-01-01	80.625