Year	Percent
1970-01-01	63.1
1971-01-01	62.6
1972-01-01	62.4
1973-01-01	62.5
1974-01-01	63.6
1975-01-01	64.8
1976-01-01	64.9
1977-01-01	64.8
1978-01-01	64.6
1979-01-01	65.3
1980-01-01	65.6
1981-01-01	65.1
1982-01-01	64.7
1983-01-01	64.4
1984-01-01	64.5
1985-01-01	65.0
1986-01-01	65.2
1987-01-01	65.0
1988-01-01	65.7
1989-01-01	66.2
1990-01-01	66.1
1991-01-01	64.9
1992-01-01	62.0
1993-01-01	58.5
1994-01-01	57.5
1995-01-01	58.2
1996-01-01	57.6
1997-01-01	56.9
1998-01-01	57.6
1999-01-01	58.3
2000-01-01	60.1
2001-01-01	60.5
2002-01-01	60.6
2003-01-01	60.2
2004-01-01	59.5
2005-01-01	59.8
2006-01-01	60.4
2007-01-01	61.3
2008-01-01	61.4
2009-01-01	59.4
2010-01-01	59.2
2011-01-01	60.1
2012-01-01	60.1