Year	Percent
1970-01-01	32.8
1971-01-01	33.2
1972-01-01	33.4
1973-01-01	34.1
1974-01-01	34.8
1975-01-01	35.5
1976-01-01	35.6
1977-01-01	36.1
1978-01-01	36.3
1979-01-01	36.4
1980-01-01	37.1
1981-01-01	37.2
1982-01-01	37.3
1983-01-01	37.5
1984-01-01	38.0
1985-01-01	38.6
1986-01-01	39.6
1987-01-01	40.0
1988-01-01	40.5
1989-01-01	41.1
1990-01-01	41.6
1991-01-01	41.8
1992-01-01	41.9
1993-01-01	42.1
1994-01-01	42.4
1995-01-01	42.9
1996-01-01	43.0
1997-01-01	43.1
1998-01-01	43.3
1999-01-01	43.5
2000-01-01	44.0
2001-01-01	44.3
2002-01-01	44.4
2003-01-01	44.8
2004-01-01	44.6
2005-01-01	45.0
2006-01-01	45.2
2007-01-01	45.3
2008-01-01	45.4
2009-01-01	45.5
2010-01-01	45.4
2011-01-01	45.6
2012-01-01	45.7