Year	Percent
1973-01-01	79.4
1974-01-01	79.3
1975-01-01	80.0
1976-01-01	79.2
1977-01-01	78.7
1978-01-01	77.8
1979-01-01	77.0
1980-01-01	77.4
1981-01-01	77.5
1982-01-01	76.1
1983-01-01	75.2
1984-01-01	74.3
1985-01-01	73.8
1986-01-01	72.4
1987-01-01	69.9
1988-01-01	70.1
1989-01-01	70.2
1990-01-01	70.4
1991-01-01	70.7
1992-01-01	71.0
1993-01-01	69.1
1994-01-01	69.4
1995-01-01	70.9
1996-01-01	71.2
1997-01-01	71.7
1998-01-01	72.3
1999-01-01	72.4
2000-01-01	73.1
2001-01-01	73.5
2002-01-01	73.9
2003-01-01	73.6
2004-01-01	73.5
2005-01-01	72.8
2006-01-01	72.8
2007-01-01	73.2
2008-01-01	73.2
2009-01-01	72.9
2010-01-01	71.1
2011-01-01	70.3
2012-01-01	70.9