Year	Percent
1991-01-01	13.9560003280640
1992-01-01	13.1920003890991
1993-01-01	18.4500007629395
1994-01-01	21.9150009155273
1995-01-01	21.5699996948242
1996-01-01	20.4829998016357
1997-01-01	21.2800006866455
1998-01-01	20.3799991607666
1999-01-01	22.6060009002686
2000-01-01	15.2829999923706
2001-01-01	15.3909997940063
2002-01-01	15.6899995803833
2003-01-01	19.0049991607666
2004-01-01	17.5039997100830
2005-01-01	21.4430007934570
2006-01-01	20.4400005340576
2007-01-01	18.7600002288818
2008-01-01	17.9230003356934
2009-01-01	21.9020004272461
2010-01-01	22.4029998779297
2011-01-01	18.7609996795654
2012-01-01	19.7810001373291
2013-01-01	23.7479991912842
2014-01-01	23.2269992828369
2015-01-01	22.1280002593994
2016-01-01	20.0900001525879
2017-01-01	19.2140007019043