Year	Percent
1970-01-01	4.4
1971-01-01	5.3
1972-01-01	5.0
1973-01-01	4.2
1974-01-01	4.9
1975-01-01	7.9
1976-01-01	7.1
1977-01-01	6.3
1978-01-01	5.3
1979-01-01	5.1
1980-01-01	6.9
1981-01-01	7.4
1982-01-01	9.9
1983-01-01	9.9
1984-01-01	7.4
1985-01-01	7.0
1986-01-01	6.9
1987-01-01	6.2
1988-01-01	5.5
1989-01-01	5.2
1990-01-01	5.7
1991-01-01	7.2
1992-01-01	7.9
1993-01-01	7.2
1994-01-01	6.2
1995-01-01	5.6
1996-01-01	5.4
1997-01-01	4.9
1998-01-01	4.4
1999-01-01	4.1
2000-01-01	3.9
2001-01-01	4.8
2002-01-01	5.9
2003-01-01	6.3
2004-01-01	5.6
2005-01-01	5.1
2006-01-01	4.6
2007-01-01	4.7
2008-01-01	6.1
2009-01-01	10.3
2010-01-01	10.5
2011-01-01	9.4
2012-01-01	8.2