Year	Percent
1970-01-01	57.3
1971-01-01	57.9
1972-01-01	58.6
1973-01-01	59.3
1974-01-01	60.1
1975-01-01	61.5
1976-01-01	62.4
1977-01-01	62.9
1978-01-01	64.3
1979-01-01	64.5
1980-01-01	64.9
1981-01-01	65.2
1982-01-01	66.1
1983-01-01	67.4
1984-01-01	68.2
1985-01-01	69.1
1986-01-01	69.8
1987-01-01	70.3
1988-01-01	70.3
1989-01-01	70.3
1990-01-01	71.2
1991-01-01	72.5
1992-01-01	73.0
1993-01-01	72.8
1994-01-01	73.1
1995-01-01	73.7
1996-01-01	73.9
1997-01-01	74.1
1998-01-01	74.5
1999-01-01	74.9
2000-01-01	74.4
2001-01-01	75.4
2002-01-01	75.6
2003-01-01	76.2
2004-01-01	76.0
2005-01-01	76.3
2006-01-01	76.3
2007-01-01	76.5
2008-01-01	76.2
2009-01-01	76.7
2010-01-01	77.0
2011-01-01	77.6
2012-01-01	77.7