Year	Percent
1970-01-01	76.2
1971-01-01	74.9
1972-01-01	75.0
1973-01-01	75.5
1974-01-01	74.9
1975-01-01	71.7
1976-01-01	72.0
1977-01-01	72.8
1978-01-01	73.8
1979-01-01	73.8
1980-01-01	72.0
1981-01-01	71.3
1982-01-01	69.0
1983-01-01	68.8
1984-01-01	70.7
1985-01-01	70.9
1986-01-01	71.0
1987-01-01	71.5
1988-01-01	72.0
1989-01-01	72.5
1990-01-01	72.0
1991-01-01	70.4
1992-01-01	69.8
1993-01-01	70.0
1994-01-01	70.4
1995-01-01	70.8
1996-01-01	70.9
1997-01-01	71.3
1998-01-01	71.6
1999-01-01	71.6
2000-01-01	71.9
2001-01-01	70.9
2002-01-01	69.7
2003-01-01	68.9
2004-01-01	69.2
2005-01-01	69.6
2006-01-01	70.1
2007-01-01	69.8
2008-01-01	68.5
2009-01-01	64.5
2010-01-01	63.7
2011-01-01	63.9
2012-01-01	64.4