Year	Percent
1970-01-01	61.1
1971-01-01	61.0
1972-01-01	60.6
1973-01-01	61.2
1974-01-01	61.3
1975-01-01	60.1
1976-01-01	59.7
1977-01-01	59.2
1978-01-01	58.0
1979-01-01	57.8
1980-01-01	58.3
1981-01-01	58.4
1982-01-01	57.3
1983-01-01	55.3
1984-01-01	56.0
1985-01-01	56.6
1986-01-01	57.8
1987-01-01	57.8
1988-01-01	58.8
1989-01-01	60.2
1990-01-01	60.2
1991-01-01	58.0
1992-01-01	57.0
1993-01-01	56.6
1994-01-01	57.7
1995-01-01	59.1
1996-01-01	59.1
1997-01-01	58.9
1998-01-01	59.3
1999-01-01	59.6
2000-01-01	60.3
2001-01-01	60.0
2002-01-01	60.2
2003-01-01	60.8
2004-01-01	61.1
2005-01-01	62.1
2006-01-01	62.7
2007-01-01	63.3
2008-01-01	63.9
2009-01-01	63.0
2010-01-01	63.0
2011-01-01	63.1
2012-01-01	62.7