Year	Percent
1971-01-01	37.3
1972-01-01	37.6
1973-01-01	38.1
1974-01-01	38.6
1975-01-01	38.8
1976-01-01	38.9
1977-01-01	39.2
1978-01-01	39.6
1979-01-01	40.0
1980-01-01	40.4
1981-01-01	40.5
1982-01-01	40.7
1983-01-01	41.1
1984-01-01	41.8
1985-01-01	42.1
1986-01-01	42.6
1987-01-01	42.9
1988-01-01	43.2
1989-01-01	43.5
1990-01-01	43.7
1991-01-01	43.8
1992-01-01	44.0
1993-01-01	44.3
1994-01-01	44.5
1995-01-01	44.7
1996-01-01	44.9
1997-01-01	45.1
1998-01-01	45.3
1999-01-01	45.4
2000-01-01	45.6
2001-01-01	45.6
2002-01-01	45.7
2003-01-01	45.7
2004-01-01	45.8
2005-01-01	45.9
2006-01-01	46.0
2007-01-01	45.8
2008-01-01	45.8
2009-01-01	46.0
2010-01-01	46.1
2011-01-01	46.2
2012-01-01	46.2