Year	Percent
1970-01-01	57.4
1971-01-01	56.6
1972-01-01	57.0
1973-01-01	57.8
1974-01-01	57.8
1975-01-01	56.1
1976-01-01	56.8
1977-01-01	57.9
1978-01-01	59.3
1979-01-01	59.9
1980-01-01	59.2
1981-01-01	59.0
1982-01-01	57.8
1983-01-01	57.9
1984-01-01	59.5
1985-01-01	60.1
1986-01-01	60.7
1987-01-01	61.5
1988-01-01	62.3
1989-01-01	63.0
1990-01-01	62.8
1991-01-01	61.7
1992-01-01	61.5
1993-01-01	61.7
1994-01-01	62.5
1995-01-01	62.9
1996-01-01	63.2
1997-01-01	63.8
1998-01-01	64.1
1999-01-01	64.3
2000-01-01	64.4
2001-01-01	63.7
2002-01-01	62.7
2003-01-01	62.3
2004-01-01	62.3
2005-01-01	62.7
2006-01-01	63.1
2007-01-01	63.0
2008-01-01	62.2
2009-01-01	59.3
2010-01-01	58.5
2011-01-01	58.4
2012-01-01	58.6