Year	Percent
1970-01-01	54.5
1971-01-01	54.5
1972-01-01	54.9
1973-01-01	56.4
1974-01-01	57.3
1975-01-01	56.9
1976-01-01	58.2
1977-01-01	57.9
1978-01-01	58.5
1979-01-01	59.8
1980-01-01	60.3
1981-01-01	60.8
1982-01-01	58.0
1983-01-01	57.6
1984-01-01	58.3
1985-01-01	59.4
1986-01-01	60.3
1987-01-01	61.2
1988-01-01	62.2
1989-01-01	62.7
1990-01-01	62.2
1991-01-01	60.2
1992-01-01	58.9
1993-01-01	58.5
1994-01-01	59.0
1995-01-01	59.3
1996-01-01	59.1
1997-01-01	59.7
1998-01-01	60.4
1999-01-01	61.3
2000-01-01	62.0
2001-01-01	61.8
2002-01-01	62.4
2003-01-01	63.1
2004-01-01	63.3
2005-01-01	63.3
2006-01-01	63.5
2007-01-01	64.0
2008-01-01	64.1
2009-01-01	62.2
2010-01-01	62.3
2011-01-01	62.5
2012-01-01	62.5