Year	Percent
1989-01-01	18.9
1993-01-01	22.0
1995-01-01	20.1
1996-01-01	19.8
1997-01-01	19.2
1998-01-01	18.2
1999-01-01	16.5
2000-01-01	15.5
2001-01-01	15.8
2002-01-01	16.2
2003-01-01	17.2
2004-01-01	17.3
2005-01-01	18.4
2006-01-01	18.2
2007-01-01	17.9
2008-01-01	18.0
2009-01-01	19.8
2010-01-01	21.4
2011-01-01	22.3
2012-01-01	22.4
2013-01-01	22.0
2014-01-01	21.5
2015-01-01	20.5
2016-01-01	19.3