Year	Percent
1970-01-01	79.7
1971-01-01	79.1
1972-01-01	78.9
1973-01-01	78.8
1974-01-01	78.7
1975-01-01	77.9
1976-01-01	77.5
1977-01-01	77.7
1978-01-01	77.9
1979-01-01	77.8
1980-01-01	77.4
1981-01-01	77.0
1982-01-01	76.6
1983-01-01	76.4
1984-01-01	76.4
1985-01-01	76.3
1986-01-01	76.3
1987-01-01	76.2
1988-01-01	76.2
1989-01-01	76.4
1990-01-01	76.4
1991-01-01	75.8
1992-01-01	75.8
1993-01-01	75.4
1994-01-01	75.1
1995-01-01	75.0
1996-01-01	74.9
1997-01-01	75.0
1998-01-01	74.9
1999-01-01	74.7
2000-01-01	74.8
2001-01-01	74.4
2002-01-01	74.1
2003-01-01	73.5
2004-01-01	73.3
2005-01-01	73.3
2006-01-01	73.5
2007-01-01	73.2
2008-01-01	73.0
2009-01-01	72.0
2010-01-01	71.2
2011-01-01	70.5
2012-01-01	70.2