Year	Percent
1970-01-01	1.5
1971-01-01	2.6
1972-01-01	2.7
1973-01-01	2.5
1974-01-01	2.0
1975-01-01	1.6
1976-01-01	1.6
1977-01-01	1.8
1978-01-01	2.2
1979-01-01	2.1
1980-01-01	2.0
1981-01-01	2.5
1982-01-01	3.1
1983-01-01	3.5
1984-01-01	3.1
1985-01-01	2.8
1986-01-01	2.6
1987-01-01	2.3
1988-01-01	1.9
1989-01-01	1.6
1990-01-01	1.8
1991-01-01	3.2
1992-01-01	5.8
1993-01-01	9.4
1994-01-01	9.6
1995-01-01	9.1
1996-01-01	9.9
1997-01-01	10.1
1998-01-01	8.4
1999-01-01	7.1
2000-01-01	5.8
2001-01-01	5.0
2002-01-01	5.1
2003-01-01	5.8
2004-01-01	6.6
2005-01-01	7.7
2006-01-01	7.0
2007-01-01	6.1
2008-01-01	6.1
2009-01-01	8.3
2010-01-01	8.5
2011-01-01	7.7
2012-01-01	7.9