Year	Percent
1970-01-01	73.4
1971-01-01	72.7
1972-01-01	73.0
1973-01-01	74.3
1974-01-01	74.9
1975-01-01	73.5
1976-01-01	74.2
1977-01-01	73.3
1978-01-01	73.4
1979-01-01	74.3
1980-01-01	74.0
1981-01-01	73.9
1982-01-01	69.3
1983-01-01	68.3
1984-01-01	68.9
1985-01-01	69.6
1986-01-01	70.4
1987-01-01	71.0
1988-01-01	71.6
1989-01-01	71.8
1990-01-01	70.6
1991-01-01	67.6
1992-01-01	65.7
1993-01-01	65.3
1994-01-01	65.9
1995-01-01	66.1
1996-01-01	65.8
1997-01-01	66.4
1998-01-01	66.8
1999-01-01	67.5
2000-01-01	68.2
2001-01-01	67.7
2002-01-01	67.9
2003-01-01	68.3
2004-01-01	68.5
2005-01-01	68.6
2006-01-01	68.4
2007-01-01	68.7
2008-01-01	68.8
2009-01-01	65.9
2010-01-01	66.2
2011-01-01	66.6
2012-01-01	66.6