Year	Percent
1970-01-01	49.1
1971-01-01	49.5
1972-01-01	50.0
1973-01-01	50.3
1974-01-01	52.0
1975-01-01	54.1
1976-01-01	54.7
1977-01-01	55.5
1978-01-01	56.1
1979-01-01	57.2
1980-01-01	58.0
1981-01-01	58.5
1982-01-01	58.4
1983-01-01	58.6
1984-01-01	59.1
1985-01-01	59.7
1986-01-01	60.1
1987-01-01	60.5
1988-01-01	61.2
1989-01-01	61.7
1990-01-01	61.8
1991-01-01	60.6
1992-01-01	58.4
1993-01-01	55.5
1994-01-01	54.3
1995-01-01	54.7
1996-01-01	53.9
1997-01-01	53.0
1998-01-01	53.3
1999-01-01	54.2
2000-01-01	56.1
2001-01-01	56.7
2002-01-01	57.1
2003-01-01	56.8
2004-01-01	56.1
2005-01-01	56.0
2006-01-01	56.4
2007-01-01	57.3
2008-01-01	57.3
2009-01-01	56.0
2010-01-01	55.2
2011-01-01	56.3
2012-01-01	56.7