Year	Percent
1971-01-01	3.1
1972-01-01	2.9
1973-01-01	2.9
1974-01-01	2.7
1975-01-01	2.7
1976-01-01	2.7
1977-01-01	2.7
1978-01-01	2.7
1979-01-01	2.6
1980-01-01	2.5
1981-01-01	2.6
1982-01-01	2.6
1983-01-01	2.6
1984-01-01	2.5
1985-01-01	2.2
1986-01-01	2.1
1987-01-01	2.2
1988-01-01	2.2
1989-01-01	2.1
1990-01-01	2.0
1991-01-01	2.2
1992-01-01	2.1
1993-01-01	1.9
1994-01-01	2.0
1995-01-01	2.0
1996-01-01	1.9
1997-01-01	1.6
1998-01-01	1.4
1999-01-01	1.2
2000-01-01	1.2
2001-01-01	1.1
2002-01-01	1.0
2003-01-01	1.0
2004-01-01	0.9
2005-01-01	1.0
2006-01-01	1.0
2007-01-01	1.0
2008-01-01	1.1
2009-01-01	1.1
2010-01-01	1.2
2011-01-01	1.2
2012-01-01	1.2