Year	Percent
1971-01-01	44.7
1972-01-01	45.4
1973-01-01	46.3
1974-01-01	47.3
1975-01-01	48.2
1976-01-01	49.5
1977-01-01	50.4
1978-01-01	51.5
1979-01-01	52.4
1980-01-01	53.2
1981-01-01	54.1
1982-01-01	56.9
1983-01-01	57.8
1984-01-01	58.9
1985-01-01	60.2
1986-01-01	61.4
1987-01-01	62.2
1988-01-01	62.8
1989-01-01	63.3
1990-01-01	63.6
1991-01-01	64.2
1992-01-01	65.4
1993-01-01	66.8
1994-01-01	67.7
1995-01-01	68.4
1996-01-01	69.1
1997-01-01	69.4
1998-01-01	69.8
1999-01-01	70.2
2000-01-01	70.8
2001-01-01	70.9
2002-01-01	71.4
2003-01-01	71.9
2004-01-01	72.6
2005-01-01	73.1
2006-01-01	73.1
2007-01-01	73.7
2008-01-01	75.0
2009-01-01	75.6
2010-01-01	76.1
2011-01-01	76.1
2012-01-01	76.6