Year	Percent
1970-01-01	64.5
1971-01-01	64.2
1972-01-01	63.8
1973-01-01	64.0
1974-01-01	63.1
1975-01-01	62.4
1976-01-01	62.4
1977-01-01	62.5
1978-01-01	62.8
1979-01-01	62.7
1980-01-01	62.6
1981-01-01	62.6
1982-01-01	62.7
1983-01-01	63.1
1984-01-01	62.7
1985-01-01	62.2
1986-01-01	62.1
1987-01-01	61.8
1988-01-01	61.8
1989-01-01	62.1
1990-01-01	62.6
1991-01-01	63.1
1992-01-01	63.3
1993-01-01	63.2
1994-01-01	62.9
1995-01-01	62.8
1996-01-01	62.8
1997-01-01	63.0
1998-01-01	62.6
1999-01-01	62.0
2000-01-01	61.7
2001-01-01	61.2
2002-01-01	60.4
2003-01-01	59.9
2004-01-01	59.6
2005-01-01	59.5
2006-01-01	59.6
2007-01-01	59.8
2008-01-01	59.6
2009-01-01	59.3
2010-01-01	59.1
2011-01-01	58.7
2012-01-01	58.4