Year	Percent
1970-01-01	0.4
1971-01-01	0.6
1972-01-01	0.7
1973-01-01	0.8
1974-01-01	2.2
1975-01-01	4.7
1976-01-01	4.8
1977-01-01	5.0
1978-01-01	4.5
1979-01-01	3.6
1980-01-01	3.7
1981-01-01	5.7
1982-01-01	8.2
1983-01-01	9.6
1984-01-01	10.7
1985-01-01	10.0
1986-01-01	8.0
1987-01-01	7.4
1988-01-01	6.9
1989-01-01	5.5
1990-01-01	4.6
1991-01-01	5.6
1992-01-01	6.4
1993-01-01	7.8
1994-01-01	8.5
1995-01-01	8.4
1996-01-01	9.7
1997-01-01	10.6
1998-01-01	9.4
1999-01-01	8.8
2000-01-01	8.6
2001-01-01	8.5
2002-01-01	10.0
2003-01-01	10.8
2004-01-01	12.9
2005-01-01	15.5
2006-01-01	13.8
2007-01-01	11.9
2008-01-01	10.5
2009-01-01	11.2
2010-01-01	9.8
2011-01-01	8.7
2012-01-01	8.2