Year	Percent
1970-01-01	0.5
1971-01-01	0.6
1972-01-01	0.7
1973-01-01	0.8
1974-01-01	2.1
1975-01-01	4.9
1976-01-01	5.0
1977-01-01	5.1
1978-01-01	4.8
1979-01-01	4.0
1980-01-01	3.9
1981-01-01	5.8
1982-01-01	8.4
1983-01-01	10.2
1984-01-01	9.5
1985-01-01	9.2
1986-01-01	7.6
1987-01-01	7.1
1988-01-01	6.7
1989-01-01	5.2
1990-01-01	4.4
1991-01-01	5.8
1992-01-01	6.9
1993-01-01	8.7
1994-01-01	9.5
1995-01-01	9.0
1996-01-01	10.4
1997-01-01	11.3
1998-01-01	9.9
1999-01-01	9.4
2000-01-01	8.9
2001-01-01	9.1
2002-01-01	10.9
2003-01-01	12.1
2004-01-01	14.2
2005-01-01	15.8
2006-01-01	13.6
2007-01-01	11.5
2008-01-01	10.3
2009-01-01	11.1
2010-01-01	9.5
2011-01-01	8.2
2012-01-01	7.9