Year	Percent
1970-01-01	78.8
1971-01-01	77.5
1972-01-01	76.4
1973-01-01	75.8
1974-01-01	74.6
1975-01-01	73.3
1976-01-01	72.5
1977-01-01	71.9
1978-01-01	71.6
1979-01-01	71.5
1980-01-01	71.2
1981-01-01	70.9
1982-01-01	70.6
1983-01-01	70.1
1984-01-01	70.0
1985-01-01	70.1
1986-01-01	70.2
1987-01-01	69.9
1988-01-01	69.6
1989-01-01	69.1
1990-01-01	68.5
1991-01-01	71.1
1992-01-01	70.1
1993-01-01	69.3
1994-01-01	68.8
1995-01-01	68.1
1996-01-01	67.8
1997-01-01	67.6
1998-01-01	67.9
1999-01-01	66.1
2000-01-01	65.6
2001-01-01	65.3
2002-01-01	64.6
2003-01-01	63.7
2004-01-01	64.1
2005-01-01	65.2
2006-01-01	65.5
2007-01-01	65.4
2008-01-01	65.4
2009-01-01	65.3
2010-01-01	65.1
2011-01-01	65.6
2012-01-01	65.5