Year	Percent
1989-01-01	19.6
1993-01-01	22.7
1995-01-01	20.8
1996-01-01	20.5
1997-01-01	19.9
1998-01-01	18.9
1999-01-01	17.1
2000-01-01	16.2
2001-01-01	16.3
2002-01-01	16.7
2003-01-01	17.6
2004-01-01	17.8
2005-01-01	18.5
2006-01-01	18.3
2007-01-01	18.0
2008-01-01	18.2
2009-01-01	20.0
2010-01-01	21.6
2011-01-01	22.5
2012-01-01	22.6
2013-01-01	22.2
2014-01-01	21.7
2015-01-01	20.7
2016-01-01	19.5