Year	Percent
1989-01-01	20.3
1993-01-01	23.4
1995-01-01	21.5
1996-01-01	21.1
1997-01-01	20.6
1998-01-01	19.6
1999-01-01	17.8
2000-01-01	16.8
2001-01-01	16.7
2002-01-01	17.2
2003-01-01	18.1
2004-01-01	18.3
2005-01-01	18.7
2006-01-01	18.5
2007-01-01	18.2
2008-01-01	18.4
2009-01-01	20.2
2010-01-01	21.8
2011-01-01	22.7
2012-01-01	22.8
2013-01-01	22.4
2014-01-01	21.9
2015-01-01	20.9
2016-01-01	19.7