Year	Percent
1960-01-01	33.780
1961-01-01	34.145
1962-01-01	36.265
1963-01-01	41.745
1964-01-01	46.755
1965-01-01	42.840
1966-01-01	44.650
1967-01-01	48.275
1968-01-01	49.450
1969-01-01	47.235
1970-01-01	46.560
1971-01-01	46.775
1972-01-01	48.490
1973-01-01	48.465
1974-01-01	52.075
1975-01-01	52.970
1976-01-01	51.625
1977-01-01	53.145
1978-01-01	54.930
1979-01-01	58.935
1980-01-01	61.020
1981-01-01	60.505
1982-01-01	59.980
1983-01-01	60.775
1984-01-01	58.435
1985-01-01	58.955
1986-01-01	59.210
1987-01-01	60.760
1988-01-01	58.960
1989-01-01	58.765
1990-01-01	58.840
1991-01-01	56.550
1992-01-01	57.740
1993-01-01	56.555
1994-01-01	56.670
1995-01-01	57.550
1996-01-01	61.450
1997-01-01	61.980
1998-01-01	49.840
1999-01-01	49.215
2000-01-01	71.590
2001-01-01	59.610
2002-01-01	60.460
2003-01-01	62.380
2004-01-01	62.500
2005-01-01	64.260
2006-01-01	66.360
2007-01-01	70.630
2008-01-01	78.380
2009-01-01	82.400
2010-01-01	79.040
2011-01-01	76.880
2012-01-01	76.880
2013-01-01	77.970
2014-01-01	78.950
2015-01-01	79.820