Year	Percent
1970-01-01	5.8
1971-01-01	6.6
1972-01-01	7.0
1973-01-01	6.7
1974-01-01	6.4
1975-01-01	8.1
1976-01-01	7.9
1977-01-01	8.8
1978-01-01	9.1
1979-01-01	8.3
1980-01-01	7.9
1981-01-01	7.8
1982-01-01	10.1
1983-01-01	10.8
1984-01-01	10.7
1985-01-01	9.9
1986-01-01	9.1
1987-01-01	8.6
1988-01-01	7.6
1989-01-01	7.1
1990-01-01	7.5
1991-01-01	9.0
1992-01-01	9.4
1993-01-01	9.9
1994-01-01	8.8
1995-01-01	8.0
1996-01-01	8.2
1997-01-01	8.0
1998-01-01	7.2
1999-01-01	6.6
2000-01-01	5.8
2001-01-01	6.0
2002-01-01	6.4
2003-01-01	6.3
2004-01-01	6.0
2005-01-01	5.6
2006-01-01	5.2
2007-01-01	4.8
2008-01-01	4.8
2009-01-01	6.1
2010-01-01	6.2
2011-01-01	5.9
2012-01-01	5.8