Year	Percent
1970-01-01	1.2
1971-01-01	1.3
1972-01-01	1.4
1973-01-01	1.3
1974-01-01	1.4
1975-01-01	1.9
1976-01-01	2.0
1977-01-01	2.0
1978-01-01	2.3
1979-01-01	2.1
1980-01-01	2.0
1981-01-01	2.2
1982-01-01	2.4
1983-01-01	2.7
1984-01-01	2.8
1985-01-01	2.5
1986-01-01	2.7
1987-01-01	2.6
1988-01-01	2.4
1989-01-01	2.2
1990-01-01	2.0
1991-01-01	2.0
1992-01-01	2.1
1993-01-01	2.4
1994-01-01	2.6
1995-01-01	2.9
1996-01-01	3.1
1997-01-01	3.1
1998-01-01	3.8
1999-01-01	4.2
2000-01-01	4.4
2001-01-01	4.5
2002-01-01	4.9
2003-01-01	4.6
2004-01-01	4.2
2005-01-01	3.8
2006-01-01	3.6
2007-01-01	3.6
2008-01-01	3.7
2009-01-01	4.8
2010-01-01	4.7
2011-01-01	4.2
2012-01-01	3.9