Year	Percent
1989-01-01	21.7
1993-01-01	26.5
1995-01-01	24.2
1996-01-01	23.4
1997-01-01	21.7
1998-01-01	20.8
1999-01-01	18.9
2000-01-01	18.7
2001-01-01	18.6
2002-01-01	19.0
2003-01-01	20.3
2004-01-01	20.5
2005-01-01	21.3
2006-01-01	21.0
2007-01-01	20.8
2008-01-01	21.2
2009-01-01	23.2
2010-01-01	25.0
2011-01-01	25.8
2012-01-01	25.6
2013-01-01	24.8
2014-01-01	23.9
2015-01-01	22.8
2016-01-01	21.3