Year	Percent
1989-01-01	17.7
1993-01-01	20.4
1995-01-01	18.7
1996-01-01	18.6
1997-01-01	18.4
1998-01-01	17.5
1999-01-01	15.9
2000-01-01	14.6
2001-01-01	14.8
2002-01-01	15.3
2003-01-01	16.1
2004-01-01	16.2
2005-01-01	17.0
2006-01-01	16.7
2007-01-01	16.4
2008-01-01	16.5
2009-01-01	18.2
2010-01-01	19.8
2011-01-01	20.8
2012-01-01	21.0
2013-01-01	20.8
2014-01-01	20.4
2015-01-01	19.5
2016-01-01	18.3