Year	Percent
1973-01-01	6.1
1974-01-01	6.0
1975-01-01	5.9
1976-01-01	5.7
1977-01-01	5.6
1978-01-01	5.6
1979-01-01	5.4
1980-01-01	5.2
1981-01-01	5.2
1982-01-01	5.3
1983-01-01	5.3
1984-01-01	5.2
1985-01-01	5.1
1986-01-01	5.0
1987-01-01	4.9
1988-01-01	4.8
1989-01-01	4.7
1990-01-01	4.7
1991-01-01	4.6
1992-01-01	4.1
1993-01-01	4.0
1994-01-01	4.1
1995-01-01	3.9
1996-01-01	4.0
1997-01-01	3.8
1998-01-01	3.4
1999-01-01	3.2
2000-01-01	3.2
2001-01-01	3.0
2002-01-01	3.0
2003-01-01	3.0
2004-01-01	3.1
2005-01-01	3.3
2006-01-01	3.3
2007-01-01	3.0
2008-01-01	2.7
2009-01-01	2.7
2010-01-01	3.1
2011-01-01	2.8
2012-01-01	2.8