Year	Percent
1973-01-01	77.3
1974-01-01	77.1
1975-01-01	76.9
1976-01-01	75.9
1977-01-01	75.7
1978-01-01	75.0
1979-01-01	74.3
1980-01-01	74.1
1981-01-01	72.2
1982-01-01	69.5
1983-01-01	67.4
1984-01-01	66.6
1985-01-01	67.6
1986-01-01	66.7
1987-01-01	64.8
1988-01-01	65.0
1989-01-01	65.7
1990-01-01	66.5
1991-01-01	66.8
1992-01-01	67.2
1993-01-01	65.5
1994-01-01	65.2
1995-01-01	66.7
1996-01-01	67.5
1997-01-01	68.5
1998-01-01	69.8
1999-01-01	70.4
2000-01-01	71.4
2001-01-01	72.0
2002-01-01	71.9
2003-01-01	70.6
2004-01-01	70.0
2005-01-01	69.2
2006-01-01	70.0
2007-01-01	70.9
2008-01-01	71.2
2009-01-01	70.2
2010-01-01	67.9
2011-01-01	67.1
2012-01-01	67.1