Year	Percent
1998-01-01	39.475
1999-01-01	39.325
2000-01-01	38.900
2001-01-01	38.425
2002-01-01	38.025
2003-01-01	38.050
2004-01-01	38.425
2005-01-01	38.125
2006-01-01	37.950
2007-01-01	37.775
2008-01-01	37.950
2009-01-01	38.650
2010-01-01	38.750
2011-01-01	39.475
2012-01-01	39.825
2013-01-01	40.700
2014-01-01	41.150
2015-01-01	41.425
2016-01-01	41.550
2017-01-01	41.050