Year	Percent
1970-01-01	84.1
1971-01-01	83.8
1972-01-01	83.6
1973-01-01	83.1
1974-01-01	82.7
1975-01-01	82.2
1976-01-01	81.5
1977-01-01	81.0
1978-01-01	79.8
1979-01-01	79.5
1980-01-01	79.1
1981-01-01	78.8
1982-01-01	78.4
1983-01-01	77.6
1984-01-01	77.3
1985-01-01	76.7
1986-01-01	76.7
1987-01-01	76.2
1988-01-01	76.0
1989-01-01	76.4
1990-01-01	76.5
1991-01-01	75.6
1992-01-01	75.1
1993-01-01	74.5
1994-01-01	74.5
1995-01-01	74.7
1996-01-01	74.5
1997-01-01	74.0
1998-01-01	73.7
1999-01-01	73.4
2000-01-01	73.1
2001-01-01	72.7
2002-01-01	72.5
2003-01-01	72.4
2004-01-01	72.6
2005-01-01	73.0
2006-01-01	73.2
2007-01-01	73.3
2008-01-01	73.6
2009-01-01	73.3
2010-01-01	73.2
2011-01-01	73.1
2012-01-01	72.6