Year	Percent
1989-01-01	12.8
1993-01-01	15.1
1995-01-01	13.8
1996-01-01	13.7
1997-01-01	13.3
1998-01-01	12.7
1999-01-01	11.9
2000-01-01	11.3
2001-01-01	11.7
2002-01-01	12.1
2003-01-01	12.5
2004-01-01	12.7
2005-01-01	13.3
2006-01-01	13.3
2007-01-01	13.0
2008-01-01	13.2
2009-01-01	14.3
2010-01-01	15.3
2011-01-01	15.9
2012-01-01	15.9
2013-01-01	15.8
2014-01-01	15.5
2015-01-01	14.7
2016-01-01	14