Year	Percent
1978-01-01	4.9
1979-01-01	5.6
1980-01-01	5.8
1981-01-01	7.0
1982-01-01	8.0
1983-01-01	7.2
1984-01-01	8.5
1985-01-01	9.0
1986-01-01	9.1
1987-01-01	9.3
1988-01-01	8.8
1989-01-01	8.4
1990-01-01	8.0
1991-01-01	8.4
1992-01-01	9.3
1993-01-01	10.6
1994-01-01	11.1
1995-01-01	10.5
1996-01-01	11.0
1997-01-01	11.1
1998-01-01	10.8
1999-01-01	10.4
2000-01-01	9.0
2001-01-01	8.2
2002-01-01	8.3
2003-01-01	8.9
2004-01-01	9.3
2005-01-01	9.3
2006-01-01	9.2
2007-01-01	8.4
2008-01-01	7.8
2009-01-01	9.5
2010-01-01	9.8
2011-01-01	9.7