Year	Percent of Total
1960-01-01	54.7322063871713
1961-01-01	53.9216452230363
1962-01-01	53.4510114464255
1963-01-01	53.3122864433662
1964-01-01	53.4299667537570
1965-01-01	53.7247151998500
1966-01-01	54.4176738214778
1967-01-01	55.1578423934741
1968-01-01	55.9660487984672
1969-01-01	56.8796300665314
1970-01-01	57.8953235309730
1971-01-01	58.9282677435782
1972-01-01	59.9282779452822
1973-01-01	60.9330778874105
1974-01-01	61.9867283745448
1975-01-01	63.1031867270156
1976-01-01	64.0318792356812
1977-01-01	65.1481307896493
1978-01-01	66.3314582675793
1979-01-01	67.3955108603798
1980-01-01	68.2329062487042
1981-01-01	69.0222310555209
1982-01-01	69.5080472152016
1983-01-01	69.7954974322365
1984-01-01	70.0742562929494
1985-01-01	70.4452908574459
1986-01-01	70.8926689171219
1987-01-01	71.5071033100073
1988-01-01	72.1603035498030
1989-01-01	72.6709914483869
1990-01-01	72.9410316058697
1991-01-01	72.8771834642847
1992-01-01	72.5648728159519
1993-01-01	72.0999407468332
1994-01-01	71.6710532145864
1995-01-01	71.4039034960255
1996-01-01	71.0122981952720
1997-01-01	70.8943078291157
1998-01-01	70.9780674484917
1999-01-01	71.1140506308561
2000-01-01	71.1986836860878
2001-01-01	71.5978659189769
2002-01-01	71.9409189757572
2003-01-01	72.2220980186125
2004-01-01	72.4565450201829
2005-01-01	72.6263303705465
2006-01-01	72.6937330181199
2007-01-01	72.8030769178756
2008-01-01	73.0250959110587
2009-01-01	73.3332151852032
2010-01-01	73.6399177652194
2011-01-01	73.6326793362541
2012-01-01	73.5270324673428
2013-01-01	73.3420919158706
2014-01-01	73.1005322353112
2015-01-01	72.8109527606823
2016-01-01	72.4719361915747
2017-01-01	72.0967152018868