Year	Percent
1970-01-01	47.4
1971-01-01	48.5
1972-01-01	49.4
1973-01-01	49.9
1974-01-01	50.6
1975-01-01	52.0
1976-01-01	52.5
1977-01-01	53.3
1978-01-01	53.8
1979-01-01	54.5
1980-01-01	54.8
1981-01-01	55.3
1982-01-01	56.0
1983-01-01	56.6
1984-01-01	56.9
1985-01-01	57.0
1986-01-01	57.6
1987-01-01	58.5
1988-01-01	58.5
1989-01-01	58.7
1990-01-01	59.2
1991-01-01	59.4
1992-01-01	59.5
1993-01-01	60.3
1994-01-01	60.8
1995-01-01	61.4
1996-01-01	61.8
1997-01-01	62.1
1998-01-01	63.3
1999-01-01	63.8
2000-01-01	64.3
2001-01-01	65.2
2002-01-01	66.5
2003-01-01	67.1
2004-01-01	68.0
2005-01-01	68.7
2006-01-01	68.8
2007-01-01	68.9
2008-01-01	69.4
2009-01-01	70.4
2010-01-01	71.1
2011-01-01	71.3
2012-01-01	71.7