Year	Percent of Total
1960-01-01	53.2217692912823
1961-01-01	52.5902677969085
1962-01-01	51.8270256771176
1963-01-01	51.0100407055631
1964-01-01	50.4636733259972
1965-01-01	50.4519487676585
1966-01-01	50.8147432409614
1967-01-01	51.9134365768508
1968-01-01	53.5248321917220
1969-01-01	55.3097051178781
1970-01-01	57.0937671358070
1971-01-01	59.4382063126410
1972-01-01	61.4888630726744
1973-01-01	63.2892887947616
1974-01-01	64.9768302467620
1975-01-01	66.5845845680136
1976-01-01	67.5207562164084
1977-01-01	68.4294133800883
1978-01-01	69.0996522079269
1979-01-01	69.2316512300460
1980-01-01	68.7440680670928
1981-01-01	69.3768563059973
1982-01-01	69.3709472611546
1983-01-01	69.0781886381836
1984-01-01	68.9264061942771
1985-01-01	69.0360073488703
1986-01-01	68.3837430709862
1987-01-01	68.2309626145487
1988-01-01	68.2710197365346
1989-01-01	68.1908435240507
1990-01-01	67.9392908543765
1991-01-01	67.7349871665857
1992-01-01	67.4650098355952
1993-01-01	67.2281251265712
1994-01-01	67.1756270504815
1995-01-01	67.3563468728448
1996-01-01	67.6347356358638
1997-01-01	68.0033568746202
1998-01-01	68.4647799003018
1999-01-01	69.0375629473202
2000-01-01	69.7534224810096
2001-01-01	70.7912463676809
2002-01-01	72.0373984174508
2003-01-01	73.3917639363073
2004-01-01	74.7294003856164
2005-01-01	75.9600380471611
2006-01-01	77.2097218843753
2007-01-01	78.3017051623288
2008-01-01	79.2115454906017
2009-01-01	79.9348198121882
2010-01-01	80.4528753056508
2011-01-01	80.4726275346308
2012-01-01	80.3667708979594
2013-01-01	80.0965891626334
2014-01-01	79.6318155647006
2015-01-01	78.9756748571410
2016-01-01	78.0211935631943
2017-01-01	76.9379038721937