Year	Percent
1970-01-01	40.4
1971-01-01	41.0
1972-01-01	41.2
1973-01-01	42.4
1974-01-01	43.5
1975-01-01	44.5
1976-01-01	44.3
1977-01-01	44.8
1978-01-01	44.5
1979-01-01	44.3
1980-01-01	45.5
1981-01-01	45.5
1982-01-01	45.4
1983-01-01	45.5
1984-01-01	46.1
1985-01-01	47.1
1986-01-01	49.3
1987-01-01	50.0
1988-01-01	50.8
1989-01-01	52.2
1990-01-01	53.2
1991-01-01	53.0
1992-01-01	53.1
1993-01-01	52.9
1994-01-01	53.6
1995-01-01	54.7
1996-01-01	55.0
1997-01-01	54.8
1998-01-01	55.0
1999-01-01	55.0
2000-01-01	55.8
2001-01-01	56.2
2002-01-01	56.3
2003-01-01	57.1
2004-01-01	56.9
2005-01-01	58.0
2006-01-01	58.6
2007-01-01	59.3
2008-01-01	60.0
2009-01-01	60.1
2010-01-01	59.8
2011-01-01	60.0
2012-01-01	59.9