Year	Percent
1970-01-01	1.4
1971-01-01	2.4
1972-01-01	2.5
1973-01-01	2.2
1974-01-01	1.7
1975-01-01	1.3
1976-01-01	1.3
1977-01-01	1.5
1978-01-01	2.1
1979-01-01	1.9
1980-01-01	1.7
1981-01-01	2.4
1982-01-01	3.0
1983-01-01	3.4
1984-01-01	3.0
1985-01-01	2.7
1986-01-01	2.6
1987-01-01	2.3
1988-01-01	1.9
1989-01-01	1.6
1990-01-01	1.9
1991-01-01	3.5
1992-01-01	6.8
1993-01-01	11.0
1994-01-01	11.0
1995-01-01	9.9
1996-01-01	10.4
1997-01-01	10.4
1998-01-01	8.7
1999-01-01	7.4
2000-01-01	6.2
2001-01-01	5.3
2002-01-01	5.6
2003-01-01	6.3
2004-01-01	6.9
2005-01-01	7.8
2006-01-01	6.9
2007-01-01	5.8
2008-01-01	5.8
2009-01-01	8.6
2010-01-01	8.6
2011-01-01	7.8
2012-01-01	8.2