Year	Percent
1970-01-01	1.2
1971-01-01	2.0
1972-01-01	2.1
1973-01-01	1.9
1974-01-01	1.5
1975-01-01	1.2
1976-01-01	1.2
1977-01-01	1.3
1978-01-01	1.6
1979-01-01	1.5
1980-01-01	1.4
1981-01-01	1.8
1982-01-01	2.3
1983-01-01	2.6
1984-01-01	2.6
1985-01-01	2.2
1986-01-01	2.1
1987-01-01	1.7
1988-01-01	1.4
1989-01-01	1.2
1990-01-01	1.3
1991-01-01	2.4
1992-01-01	4.5
1993-01-01	7.4
1994-01-01	7.7
1995-01-01	7.6
1996-01-01	8.5
1997-01-01	8.7
1998-01-01	7.3
1999-01-01	6.2
2000-01-01	5.0
2001-01-01	4.1
2002-01-01	4.2
2003-01-01	4.8
2004-01-01	5.3
2005-01-01	5.8
2006-01-01	5.0
2007-01-01	4.3
2008-01-01	4.1
2009-01-01	5.9
2010-01-01	6.2
2011-01-01	5.5
2012-01-01	5.7