Year	Percent
1970-01-01	83.2
1971-01-01	82.7
1972-01-01	82.0
1973-01-01	81.8
1974-01-01	81.1
1975-01-01	79.1
1976-01-01	78.3
1977-01-01	77.3
1978-01-01	75.5
1979-01-01	75.3
1980-01-01	75.1
1981-01-01	75.1
1982-01-01	73.4
1983-01-01	70.1
1984-01-01	70.5
1985-01-01	70.6
1986-01-01	70.8
1987-01-01	70.3
1988-01-01	70.9
1989-01-01	72.0
1990-01-01	71.3
1991-01-01	68.1
1992-01-01	66.5
1993-01-01	65.9
1994-01-01	67.0
1995-01-01	68.1
1996-01-01	67.9
1997-01-01	67.6
1998-01-01	67.9
1999-01-01	68.2
2000-01-01	68.4
2001-01-01	67.6
2002-01-01	67.8
2003-01-01	68.1
2004-01-01	68.8
2005-01-01	69.4
2006-01-01	69.8
2007-01-01	70.4
2008-01-01	70.7
2009-01-01	69.1
2010-01-01	69.5
2011-01-01	69.5
2012-01-01	68.9