Year	Percent
1989-01-01	18.6
1993-01-01	21.3
1995-01-01	19.5
1996-01-01	19.4
1997-01-01	19.3
1998-01-01	18.3
1999-01-01	16.6
2000-01-01	15.4
2001-01-01	15.3
2002-01-01	15.9
2003-01-01	16.6
2004-01-01	16.7
2005-01-01	17.2
2006-01-01	16.9
2007-01-01	16.5
2008-01-01	16.6
2009-01-01	18.4
2010-01-01	20.0
2011-01-01	21.0
2012-01-01	21.2
2013-01-01	21.0
2014-01-01	20.6
2015-01-01	19.7
2016-01-01	18.5