Year	Percent
1989-01-01	16.9
1993-01-01	19.6
1995-01-01	17.9
1996-01-01	17.8
1997-01-01	17.6
1998-01-01	16.7
1999-01-01	15.1
2000-01-01	13.9
2001-01-01	14.3
2002-01-01	14.8
2003-01-01	15.5
2004-01-01	15.6
2005-01-01	16.8
2006-01-01	16.6
2007-01-01	16.2
2008-01-01	16.3
2009-01-01	18.1
2010-01-01	19.6
2011-01-01	20.6
2012-01-01	20.8
2013-01-01	20.6
2014-01-01	20.2
2015-01-01	19.3
2016-01-01	18.1