Year	Percent
1973-01-01	58.9
1974-01-01	59.7
1975-01-01	60.8
1976-01-01	61.9
1977-01-01	62.3
1978-01-01	62.6
1979-01-01	63.6
1980-01-01	65.1
1981-01-01	66.4
1982-01-01	67.3
1983-01-01	67.5
1984-01-01	67.5
1985-01-01	68.3
1986-01-01	68.9
1987-01-01	68.8
1988-01-01	69.5
1989-01-01	69.4
1990-01-01	69.5
1991-01-01	70.4
1992-01-01	71.6
1993-01-01	72.0
1994-01-01	73.0
1995-01-01	73.4
1996-01-01	73.7
1997-01-01	73.9
1998-01-01	75.0
1999-01-01	75.2
2000-01-01	75.5
2001-01-01	75.8
2002-01-01	76.6
2003-01-01	77.4
2004-01-01	76.9
2005-01-01	76.6
2006-01-01	77.0
2007-01-01	78.2
2008-01-01	79.4
2009-01-01	80.1
2010-01-01	80.2
2011-01-01	80.9
2012-01-01	81.0