Year	Percent
1979-01-01	5.8
1980-01-01	4.8
1981-01-01	5.5
1982-01-01	6.5
1983-01-01	7.4
1984-01-01	7.8
1985-01-01	8.2
1986-01-01	8.9
1987-01-01	9.6
1988-01-01	9.7
1989-01-01	9.7
1990-01-01	8.9
1991-01-01	8.5
1992-01-01	8.8
1993-01-01	9.8
1994-01-01	10.6
1995-01-01	11.2
1996-01-01	11.2
1997-01-01	11.2
1998-01-01	11.3
1999-01-01	10.9
2000-01-01	10.1
2001-01-01	9.1
2002-01-01	8.6
2003-01-01	8.5
2004-01-01	8.0
2005-01-01	7.7
2006-01-01	6.8
2007-01-01	6.1
2008-01-01	6.8
2009-01-01	7.8
2010-01-01	8.4
2011-01-01	8.4