Year	Percent of Total
1960-01-01	53.2543007106025
1961-01-01	52.7978394351920
1962-01-01	52.3425835478158
1963-01-01	51.9597784364745
1964-01-01	51.7470874402488
1965-01-01	51.7360228554346
1966-01-01	51.6361156223912
1967-01-01	51.7426948331680
1968-01-01	51.9915053274074
1969-01-01	52.2918636080368
1970-01-01	52.5948542488412
1971-01-01	52.7450279817117
1972-01-01	52.9260134351266
1973-01-01	53.1189976945258
1974-01-01	53.3103522046216
1975-01-01	53.4849853137225
1976-01-01	53.5594678343867
1977-01-01	53.6112191637043
1978-01-01	53.6327430071044
1979-01-01	53.6032286983864
1980-01-01	53.4970008963433
1981-01-01	53.1149635897233
1982-01-01	52.7159897402623
1983-01-01	52.3152729291990
1984-01-01	51.9489009143280
1985-01-01	51.6535705967944
1986-01-01	51.2086625447892
1987-01-01	50.9391965800193
1988-01-01	50.8565383072883
1989-01-01	50.9687220834599
1990-01-01	51.2850836314077
1991-01-01	51.5844631751374
1992-01-01	52.0142896233137
1993-01-01	52.5812893030959
1994-01-01	53.2819613186243
1995-01-01	54.1035948375555
1996-01-01	55.3498818482457
1997-01-01	56.6578191930268
1998-01-01	58.0079069642975
1999-01-01	59.4023130932550
2000-01-01	60.8547705316110
2001-01-01	62.4386468701591
2002-01-01	64.1007023339398
2003-01-01	65.8171114398585
2004-01-01	67.4968377022312
2005-01-01	69.0258008275306
2006-01-01	69.8746895176440
2007-01-01	70.5676824079731
2008-01-01	71.0741159699244
2009-01-01	71.4096740745878
2010-01-01	71.6101453352788
2011-01-01	71.7039947579851
2012-01-01	71.7172777298809
2013-01-01	71.6504718308106
2014-01-01	71.5150287665934
2015-01-01	71.3332643737431
2016-01-01	71.1112966897744
2017-01-01	70.8717398914389