Year	Percent
1971-01-01	62.8
1972-01-01	62.9
1973-01-01	63.1
1974-01-01	63.1
1975-01-01	63.1
1976-01-01	63.0
1977-01-01	62.8
1978-01-01	62.6
1979-01-01	62.7
1980-01-01	62.8
1981-01-01	62.7
1982-01-01	61.9
1983-01-01	61.6
1984-01-01	62.8
1985-01-01	62.9
1986-01-01	62.9
1987-01-01	63.2
1988-01-01	63.8
1989-01-01	64.3
1990-01-01	64.4
1991-01-01	63.7
1992-01-01	62.9
1993-01-01	62.6
1994-01-01	62.4
1995-01-01	62.4
1996-01-01	62.4
1997-01-01	62.5
1998-01-01	62.4
1999-01-01	62.8
2000-01-01	62.8
2001-01-01	62.7
2002-01-01	62.9
2003-01-01	62.9
2004-01-01	62.9
2005-01-01	63.1
2006-01-01	63.5
2007-01-01	63.4
2008-01-01	63.5
2009-01-01	63.4
2010-01-01	63.2
2011-01-01	63.2
2012-01-01	63.4