Year	Percent
1956-01-01	0.0
1957-01-01	0.0
1958-01-01	0.1
1959-01-01	0.1
1960-01-01	0.1
1961-01-01	0.0
1962-01-01	0.1
1963-01-01	0.1
1964-01-01	0.1
1965-01-01	0.1
1966-01-01	0.1
1967-01-01	0.1
1968-01-01	0.8
1969-01-01	0.3
1970-01-01	0.1
1971-01-01	0.2
1972-01-01	0.5
1973-01-01	0.2
1974-01-01	0.1
1975-01-01	0.2
1976-01-01	0.3
1977-01-01	0.3
1978-01-01	1.7
1979-01-01	1.9
1980-01-01	2.2
1981-01-01	3.6
1982-01-01	3.5
1983-01-01	5.7
1984-01-01	5.7
1985-01-01	4.2
1986-01-01	4.2
1987-01-01	4.2
1988-01-01	5.7
1989-01-01	7.3
1990-01-01	8.0
1991-01-01	10.6
1992-01-01	10.7
1993-01-01	9.8
1994-01-01	8.4
1995-01-01	6.5
1996-01-01	6.3
1997-01-01	6.8
1998-01-01	7.7
1999-01-01	7.1
2000-01-01	6.2
2001-01-01	5.5
2002-01-01	5.3
2003-01-01	4.8
2004-01-01	4.1
2005-01-01	3.8
2006-01-01	3.9
2007-01-01	3.7
2008-01-01	4.2
2009-01-01	6.1
2010-01-01	6.5
2011-01-01	6.5