Year	Percent
1970-01-01	5.6
1971-01-01	6.0
1972-01-01	5.8
1973-01-01	4.9
1974-01-01	4.8
1975-01-01	6.2
1976-01-01	6.3
1977-01-01	7.3
1978-01-01	7.5
1979-01-01	6.7
1980-01-01	6.9
1981-01-01	7.0
1982-01-01	11.1
1983-01-01	12.2
1984-01-01	11.1
1985-01-01	10.2
1986-01-01	9.3
1987-01-01	8.3
1988-01-01	7.2
1989-01-01	7.0
1990-01-01	7.9
1991-01-01	10.5
1992-01-01	11.6
1993-01-01	11.5
1994-01-01	10.2
1995-01-01	9.1
1996-01-01	9.2
1997-01-01	8.7
1998-01-01	8.0
1999-01-01	7.3
2000-01-01	6.3
2001-01-01	6.9
2002-01-01	7.6
2003-01-01	7.3
2004-01-01	6.8
2005-01-01	6.3
2006-01-01	5.8
2007-01-01	5.6
2008-01-01	5.8
2009-01-01	8.5
2010-01-01	7.8
2011-01-01	7.0
2012-01-01	6.7