Year	Percent
1970-01-01	60.4
1971-01-01	60.2
1972-01-01	60.4
1973-01-01	60.8
1974-01-01	61.3
1975-01-01	61.2
1976-01-01	61.6
1977-01-01	62.3
1978-01-01	63.2
1979-01-01	63.7
1980-01-01	63.8
1981-01-01	63.9
1982-01-01	64.0
1983-01-01	64.0
1984-01-01	64.4
1985-01-01	64.8
1986-01-01	65.3
1987-01-01	65.6
1988-01-01	65.9
1989-01-01	66.5
1990-01-01	66.5
1991-01-01	66.2
1992-01-01	66.4
1993-01-01	66.3
1994-01-01	66.6
1995-01-01	66.6
1996-01-01	66.8
1997-01-01	67.1
1998-01-01	67.1
1999-01-01	67.1
2000-01-01	67.1
2001-01-01	66.8
2002-01-01	66.6
2003-01-01	66.2
2004-01-01	66.0
2005-01-01	66.0
2006-01-01	66.2
2007-01-01	66.0
2008-01-01	66.0
2009-01-01	65.4
2010-01-01	64.7
2011-01-01	64.1
2012-01-01	63.7