Year	Percent
1970-01-01	80.5
1971-01-01	80.9
1972-01-01	80.6
1973-01-01	80.8
1974-01-01	80.5
1975-01-01	79.5
1976-01-01	79.2
1977-01-01	78.7
1978-01-01	78.2
1979-01-01	78.2
1980-01-01	77.9
1981-01-01	77.8
1982-01-01	77.4
1983-01-01	77.1
1984-01-01	76.4
1985-01-01	75.9
1986-01-01	75.4
1987-01-01	74.9
1988-01-01	75.0
1989-01-01	75.1
1990-01-01	75.4
1991-01-01	75.8
1992-01-01	76.1
1993-01-01	75.9
1994-01-01	75.4
1995-01-01	75.0
1996-01-01	74.9
1997-01-01	74.9
1998-01-01	73.9
1999-01-01	73.0
2000-01-01	72.5
2001-01-01	71.5
2002-01-01	70.4
2003-01-01	69.9
2004-01-01	69.6
2005-01-01	69.7
2006-01-01	69.9
2007-01-01	70.1
2008-01-01	69.7
2009-01-01	68.1
2010-01-01	67.7
2011-01-01	67.6
2012-01-01	67.3