Year	Percent
1970-01-01	50.0
1971-01-01	50.9
1972-01-01	51.5
1973-01-01	51.7
1974-01-01	53.3
1975-01-01	55.2
1976-01-01	55.9
1977-01-01	56.7
1978-01-01	57.5
1979-01-01	58.5
1980-01-01	59.3
1981-01-01	60.1
1982-01-01	60.5
1983-01-01	60.8
1984-01-01	61.1
1985-01-01	61.5
1986-01-01	61.7
1987-01-01	61.9
1988-01-01	62.4
1989-01-01	62.8
1990-01-01	63.0
1991-01-01	62.4
1992-01-01	61.3
1993-01-01	60.1
1994-01-01	59.2
1995-01-01	59.5
1996-01-01	59.4
1997-01-01	58.6
1998-01-01	58.0
1999-01-01	58.1
2000-01-01	59.2
2001-01-01	59.5
2002-01-01	59.9
2003-01-01	59.9
2004-01-01	59.8
2005-01-01	60.6
2006-01-01	60.8
2007-01-01	61.2
2008-01-01	61.2
2009-01-01	60.7
2010-01-01	60.3
2011-01-01	61.0
2012-01-01	61.3