Year	Percent
1984-01-01	19.8
1985-01-01	18.0
1986-01-01	18.2
1987-01-01	15.4
1988-01-01	12.6
1989-01-01	10.1
1990-01-01	10.6
1991-01-01	14.3
1992-01-01	16.3
1993-01-01	18.0
1994-01-01	16.8
1995-01-01	15.7
1996-01-01	15.4
1997-01-01	14.1
1998-01-01	13.6
1999-01-01	12.9
2000-01-01	12.4
2001-01-01	12.0
2002-01-01	12.2
2003-01-01	12.5
2004-01-01	12.4
2005-01-01	13.1
2006-01-01	14.2
2007-01-01	14.4
2008-01-01	15.2
2009-01-01	19.2
2010-01-01	19.9
2011-01-01	21.2
2012-01-01	21.2