Year	Percent
1960-01-01	47.80
1961-01-01	47.80
1962-01-01	47.28
1963-01-01	46.66
1964-01-01	46.27
1965-01-01	45.66
1966-01-01	44.97
1967-01-01	43.90
1968-01-01	43.10
1969-01-01	42.87
1970-01-01	42.81
1971-01-01	43.09
1972-01-01	43.16
1973-01-01	43.52
1974-01-01	44.01
1975-01-01	43.80
1976-01-01	44.02
1977-01-01	44.54
1978-01-01	44.80
1979-01-01	45.07
1980-01-01	45.48
1981-01-01	45.18
1982-01-01	44.54
1983-01-01	44.31
1984-01-01	44.27
1985-01-01	44.38
1986-01-01	44.49
1987-01-01	44.43
1988-01-01	44.75
1989-01-01	45.09
1990-01-01	45.61
1991-01-01	45.72
1992-01-01	45.48
1993-01-01	44.90
1994-01-01	44.74
1995-01-01	44.59
1996-01-01	44.76
1997-01-01	45.06
1998-01-01	45.47
1999-01-01	46.19
2000-01-01	46.66
2001-01-01	46.79
2002-01-01	46.51
2003-01-01	46.60
2004-01-01	46.60
2005-01-01	46.83
2006-01-01	47.37
2007-01-01	48.04
2008-01-01	48.77
2009-01-01	48.23
2010-01-01	48.51
2011-01-01	49.02