Year	Percent
1970-01-01	77.4
1971-01-01	76.1
1972-01-01	75.4
1973-01-01	75.1
1974-01-01	75.6
1975-01-01	76.0
1976-01-01	75.5
1977-01-01	74.5
1978-01-01	73.5
1979-01-01	73.7
1980-01-01	73.6
1981-01-01	72.0
1982-01-01	71.3
1983-01-01	70.4
1984-01-01	70.2
1985-01-01	70.5
1986-01-01	70.6
1987-01-01	69.7
1988-01-01	70.3
1989-01-01	70.9
1990-01-01	70.6
1991-01-01	69.2
1992-01-01	65.7
1993-01-01	61.6
1994-01-01	60.9
1995-01-01	62.0
1996-01-01	61.5
1997-01-01	61.0
1998-01-01	62.1
1999-01-01	62.5
2000-01-01	64.2
2001-01-01	64.4
2002-01-01	64.3
2003-01-01	63.7
2004-01-01	63.0
2005-01-01	63.8
2006-01-01	64.5
2007-01-01	65.4
2008-01-01	65.5
2009-01-01	63.0
2010-01-01	63.3
2011-01-01	63.9
2012-01-01	63.5