Year	Percent
1970-01-01	62.6
1971-01-01	63.1
1972-01-01	63.9
1973-01-01	63.9
1974-01-01	64.2
1975-01-01	65.8
1976-01-01	66.5
1977-01-01	67.2
1978-01-01	67.5
1979-01-01	67.4
1980-01-01	67.8
1981-01-01	68.3
1982-01-01	70.1
1983-01-01	70.8
1984-01-01	70.9
1985-01-01	71.0
1986-01-01	71.1
1987-01-01	71.3
1988-01-01	71.4
1989-01-01	71.5
1990-01-01	72.3
1991-01-01	73.6
1992-01-01	74.4
1993-01-01	75.0
1994-01-01	74.9
1995-01-01	74.8
1996-01-01	75.0
1997-01-01	74.7
1998-01-01	74.7
1999-01-01	74.8
2000-01-01	74.9
2001-01-01	75.5
2002-01-01	75.4
2003-01-01	75.7
2004-01-01	75.7
2005-01-01	75.8
2006-01-01	76.4
2007-01-01	77.1
2008-01-01	77.3
2009-01-01	78.7
2010-01-01	78.9
2011-01-01	78.8
2012-01-01	78.6