Year	Percent
1991-01-01	21.0330009460449
1992-01-01	21.7299995422363
1993-01-01	21.5690002441406
1994-01-01	21.5039997100830
1995-01-01	21.5979995727539
1996-01-01	21.7520008087158
1997-01-01	21.3640003204346
1998-01-01	21.5990009307861
1999-01-01	21.7269992828369
2000-01-01	21.4549999237061
2001-01-01	21.1359996795654
2002-01-01	21.0069999694824
2003-01-01	20.9389991760254
2004-01-01	20.5100002288818
2005-01-01	21.0380001068115
2006-01-01	21.6299991607666
2007-01-01	22.7099990844727
2008-01-01	20.1219997406006
2009-01-01	16.8199996948242
2010-01-01	16.9680004119873
2011-01-01	17.3649997711182
2012-01-01	17.2210006713867
2013-01-01	17.1930007934570
2014-01-01	17.2010002136230
2015-01-01	17.2469997406006
2016-01-01	17.2189998626709
2017-01-01	17.5520000457764