Year	Percent
1970-01-01	36.5
1971-01-01	36.8
1972-01-01	37.3
1973-01-01	37.7
1974-01-01	38.0
1975-01-01	38.5
1976-01-01	38.8
1977-01-01	39.0
1978-01-01	39.2
1979-01-01	39.3
1980-01-01	39.5
1981-01-01	39.7
1982-01-01	39.8
1983-01-01	39.8
1984-01-01	39.9
1985-01-01	40.1
1986-01-01	40.2
1987-01-01	40.3
1988-01-01	40.7
1989-01-01	41.0
1990-01-01	41.5
1991-01-01	42.8
1992-01-01	42.8
1993-01-01	42.8
1994-01-01	42.9
1995-01-01	43.1
1996-01-01	43.3
1997-01-01	43.4
1998-01-01	43.5
1999-01-01	44.0
2000-01-01	44.3
2001-01-01	44.4
2002-01-01	44.7
2003-01-01	45.0
2004-01-01	45.1
2005-01-01	45.2
2006-01-01	45.5
2007-01-01	45.7
2008-01-01	45.7
2009-01-01	45.9
2010-01-01	46.0
2011-01-01	46.2
2012-01-01	46.1