Year	Percent
1970-01-01	38.1
1971-01-01	38.2
1972-01-01	38.5
1973-01-01	38.9
1974-01-01	39.4
1975-01-01	40.0
1976-01-01	40.5
1977-01-01	41.0
1978-01-01	41.7
1979-01-01	42.1
1980-01-01	42.5
1981-01-01	43.0
1982-01-01	43.3
1983-01-01	43.5
1984-01-01	43.8
1985-01-01	44.2
1986-01-01	44.5
1987-01-01	44.8
1988-01-01	45.0
1989-01-01	45.2
1990-01-01	45.2
1991-01-01	45.3
1992-01-01	45.4
1993-01-01	45.5
1994-01-01	46.0
1995-01-01	46.1
1996-01-01	46.2
1997-01-01	46.2
1998-01-01	46.3
1999-01-01	46.5
2000-01-01	46.5
2001-01-01	46.5
2002-01-01	46.5
2003-01-01	46.6
2004-01-01	46.4
2005-01-01	46.4
2006-01-01	46.3
2007-01-01	46.4
2008-01-01	46.5
2009-01-01	46.7
2010-01-01	46.7
2011-01-01	46.6
2012-01-01	46.9