Year	Percent
1983-01-01	8.2
1984-01-01	8.9
1985-01-01	9.2
1986-01-01	8.8
1987-01-01	7.2
1988-01-01	5.9
1989-01-01	5.2
1990-01-01	4.8
1991-01-01	4.2
1992-01-01	4.1
1993-01-01	5.5
1994-01-01	6.8
1995-01-01	7.2
1996-01-01	7.2
1997-01-01	6.7
1998-01-01	5.6
1999-01-01	5.0
2000-01-01	4.5
2001-01-01	4.6
2002-01-01	5.7
2003-01-01	7.1
2004-01-01	7.5
2005-01-01	8.6
2006-01-01	8.6
2007-01-01	8.9
2008-01-01	8.5
2009-01-01	10.6
2010-01-01	12.0
2011-01-01	12.9