Year	Percent
1970-01-01	62.5
1971-01-01	64.0
1972-01-01	64.3
1973-01-01	63.9
1974-01-01	64.6
1975-01-01	66.6
1976-01-01	66.6
1977-01-01	66.7
1978-01-01	66.5
1979-01-01	66.5
1980-01-01	67.3
1981-01-01	67.8
1982-01-01	69.4
1983-01-01	71.0
1984-01-01	70.8
1985-01-01	71.3
1986-01-01	71.6
1987-01-01	72.2
1988-01-01	72.4
1989-01-01	72.6
1990-01-01	73.1
1991-01-01	73.9
1992-01-01	74.5
1993-01-01	75.1
1994-01-01	74.9
1995-01-01	74.8
1996-01-01	75.0
1997-01-01	75.0
1998-01-01	75.2
1999-01-01	75.8
2000-01-01	76.2
2001-01-01	77.1
2002-01-01	78.0
2003-01-01	78.3
2004-01-01	78.4
2005-01-01	78.6
2006-01-01	78.5
2007-01-01	78.8
2008-01-01	79.5
2009-01-01	80.9
2010-01-01	81.2
2011-01-01	81.1
2012-01-01	81.2