Year	Percent
1970-01-01	53.9
1971-01-01	55.1
1972-01-01	56.2
1973-01-01	56.6
1974-01-01	56.9
1975-01-01	57.7
1976-01-01	59.0
1977-01-01	60.2
1978-01-01	61.5
1979-01-01	62.3
1980-01-01	62.9
1981-01-01	63.8
1982-01-01	64.9
1983-01-01	65.5
1984-01-01	65.9
1985-01-01	66.1
1986-01-01	66.1
1987-01-01	66.8
1988-01-01	67.3
1989-01-01	67.3
1990-01-01	67.9
1991-01-01	69.0
1992-01-01	70.6
1993-01-01	71.6
1994-01-01	72.1
1995-01-01	71.5
1996-01-01	71.6
1997-01-01	71.9
1998-01-01	72.2
1999-01-01	72.7
2000-01-01	73.5
2001-01-01	74.3
2002-01-01	75.0
2003-01-01	75.5
2004-01-01	75.6
2005-01-01	76.6
2006-01-01	76.7
2007-01-01	76.9
2008-01-01	77.1
2009-01-01	78.6
2010-01-01	78.9
2011-01-01	79.0
2012-01-01	79.2