Year	Percent
1970-01-01	73.7
1971-01-01	73.4
1972-01-01	72.0
1973-01-01	71.2
1974-01-01	71.0
1975-01-01	70.6
1976-01-01	70.4
1977-01-01	69.5
1978-01-01	68.7
1979-01-01	68.3
1980-01-01	67.9
1981-01-01	67.8
1982-01-01	66.9
1983-01-01	66.2
1984-01-01	65.6
1985-01-01	65.3
1986-01-01	65.2
1987-01-01	64.5
1988-01-01	63.9
1989-01-01	63.4
1990-01-01	63.0
1991-01-01	63.7
1992-01-01	63.1
1993-01-01	64.3
1994-01-01	63.4
1995-01-01	62.8
1996-01-01	62.5
1997-01-01	62.3
1998-01-01	62.4
1999-01-01	62.3
2000-01-01	62.3
2001-01-01	62.0
2002-01-01	62.2
2003-01-01	61.6
2004-01-01	60.9
2005-01-01	60.6
2006-01-01	60.6
2007-01-01	60.3
2008-01-01	60.2
2009-01-01	59.4
2010-01-01	59.0
2011-01-01	58.7
2012-01-01	59.2