Year	Percent
1960-01-01	46.56
1961-01-01	46.92
1962-01-01	47.28
1963-01-01	47.49
1964-01-01	48.09
1965-01-01	48.59
1966-01-01	49.01
1967-01-01	48.59
1968-01-01	48.61
1969-01-01	49.31
1970-01-01	49.37
1971-01-01	49.05
1972-01-01	49.74
1973-01-01	50.06
1974-01-01	49.42
1975-01-01	48.63
1976-01-01	49.33
1977-01-01	49.05
1978-01-01	49.25
1979-01-01	49.60
1980-01-01	49.16
1981-01-01	48.38
1982-01-01	48.56
1983-01-01	48.61
1984-01-01	49.36
1985-01-01	50.51
1986-01-01	51.65
1987-01-01	51.80
1988-01-01	51.37
1989-01-01	51.12
1990-01-01	50.75
1991-01-01	50.39
1992-01-01	49.56
1993-01-01	48.62
1994-01-01	48.29
1995-01-01	48.81
1996-01-01	49.10
1997-01-01	49.72
1998-01-01	50.31
1999-01-01	50.63
2000-01-01	50.81
2001-01-01	51.19
2002-01-01	51.08
2003-01-01	50.35
2004-01-01	49.93
2005-01-01	50.33
2006-01-01	51.20
2007-01-01	52.39
2008-01-01	52.88
2009-01-01	51.45
2010-01-01	50.03
2011-01-01	49.69