Year	Percent
1960-01-01	50.48
1961-01-01	50.73
1962-01-01	50.91
1963-01-01	50.83
1964-01-01	50.95
1965-01-01	51.20
1966-01-01	51.81
1967-01-01	52.25
1968-01-01	52.53
1969-01-01	52.32
1970-01-01	52.27
1971-01-01	51.96
1972-01-01	51.50
1973-01-01	51.94
1974-01-01	51.03
1975-01-01	50.27
1976-01-01	50.14
1977-01-01	50.25
1978-01-01	50.28
1979-01-01	50.37
1980-01-01	50.32
1981-01-01	50.33
1982-01-01	50.39
1983-01-01	50.80
1984-01-01	50.64
1985-01-01	50.60
1986-01-01	50.59
1987-01-01	50.55
1988-01-01	50.91
1989-01-01	51.47
1990-01-01	52.15
1991-01-01	53.01
1992-01-01	53.40
1993-01-01	53.43
1994-01-01	53.35
1995-01-01	53.39
1996-01-01	53.30
1997-01-01	53.55
1998-01-01	52.79
1999-01-01	51.97
2000-01-01	51.55
2001-01-01	51.01
2002-01-01	50.32
2003-01-01	50.25
2004-01-01	50.49
2005-01-01	50.84
2006-01-01	51.06
2007-01-01	51.29
2008-01-01	51.08
2009-01-01	50.34
2010-01-01	49.97
2011-01-01	50.04