Year	Percent
1970-01-01	41.1
1971-01-01	40.9
1972-01-01	42.2
1973-01-01	43.4
1974-01-01	44.2
1975-01-01	45.1
1976-01-01	46.1
1977-01-01	46.6
1978-01-01	47.2
1979-01-01	48.2
1980-01-01	48.8
1981-01-01	50.2
1982-01-01	51.6
1983-01-01	52.6
1984-01-01	54.8
1985-01-01	56.4
1986-01-01	57.3
1987-01-01	58.1
1988-01-01	58.8
1989-01-01	59.3
1990-01-01	59.6
1991-01-01	60.2
1992-01-01	60.6
1993-01-01	61.1
1994-01-01	61.3
1995-01-01	62.0
1996-01-01	62.8
1997-01-01	63.2
1998-01-01	63.4
1999-01-01	64.0
2000-01-01	64.7
2001-01-01	65.0
2002-01-01	65.3
2003-01-01	65.3
2004-01-01	65.2
2005-01-01	65.4
2006-01-01	65.9
2007-01-01	66.1
2008-01-01	67.4
2009-01-01	68.0
2010-01-01	68.5
2011-01-01	69.0
2012-01-01	69.8