Year	Percent
1970-01-01	78.5
1971-01-01	78.0
1972-01-01	77.3
1973-01-01	76.8
1974-01-01	76.8
1975-01-01	77.0
1976-01-01	76.5
1977-01-01	75.6
1978-01-01	75.1
1979-01-01	75.1
1980-01-01	74.9
1981-01-01	73.8
1982-01-01	73.4
1983-01-01	72.9
1984-01-01	72.4
1985-01-01	72.5
1986-01-01	72.5
1987-01-01	71.3
1988-01-01	71.6
1989-01-01	72.1
1990-01-01	72.0
1991-01-01	71.7
1992-01-01	70.5
1993-01-01	69.2
1994-01-01	68.5
1995-01-01	68.8
1996-01-01	68.6
1997-01-01	68.1
1998-01-01	68.0
1999-01-01	67.5
2000-01-01	68.5
2001-01-01	68.0
2002-01-01	68.1
2003-01-01	68.0
2004-01-01	67.7
2005-01-01	69.2
2006-01-01	69.2
2007-01-01	69.5
2008-01-01	69.5
2009-01-01	68.9
2010-01-01	69.3
2011-01-01	69.3
2012-01-01	69.2