Year	Percent
1971-01-01	80.1
1972-01-01	79.6
1973-01-01	79.9
1974-01-01	79.0
1975-01-01	77.9
1976-01-01	76.7
1977-01-01	75.9
1978-01-01	75.3
1979-01-01	75.0
1980-01-01	73.3
1981-01-01	70.1
1982-01-01	68.0
1983-01-01	66.7
1984-01-01	67.3
1985-01-01	67.2
1986-01-01	66.6
1987-01-01	67.2
1988-01-01	69.0
1989-01-01	70.3
1990-01-01	70.0
1991-01-01	67.3
1992-01-01	64.8
1993-01-01	63.7
1994-01-01	64.2
1995-01-01	64.7
1996-01-01	64.8
1997-01-01	65.9
1998-01-01	66.2
1999-01-01	66.6
2000-01-01	66.9
2001-01-01	66.9
2002-01-01	66.7
2003-01-01	66.9
2004-01-01	66.9
2005-01-01	66.8
2006-01-01	66.7
2007-01-01	66.7
2008-01-01	66.4
2009-01-01	64.2
2010-01-01	63.8
2011-01-01	63.6
2012-01-01	64.0