Year	Percent
1970-01-01	0.9
1971-01-01	1.0
1972-01-01	1.1
1973-01-01	1.1
1974-01-01	1.2
1975-01-01	1.7
1976-01-01	1.8
1977-01-01	1.8
1978-01-01	2.0
1979-01-01	1.9
1980-01-01	1.8
1981-01-01	2.0
1982-01-01	2.1
1983-01-01	2.4
1984-01-01	2.4
1985-01-01	2.2
1986-01-01	2.4
1987-01-01	2.3
1988-01-01	2.0
1989-01-01	1.8
1990-01-01	1.7
1991-01-01	1.6
1992-01-01	1.7
1993-01-01	2.0
1994-01-01	2.2
1995-01-01	2.5
1996-01-01	2.6
1997-01-01	2.7
1998-01-01	3.3
1999-01-01	3.6
2000-01-01	3.8
2001-01-01	4.0
2002-01-01	4.3
2003-01-01	4.0
2004-01-01	3.7
2005-01-01	3.3
2006-01-01	3.2
2007-01-01	3.2
2008-01-01	3.3
2009-01-01	4.4
2010-01-01	4.3
2011-01-01	3.9
2012-01-01	3.5