Year	Percent of Total
1960-01-01	36.2387054821929
1961-01-01	37.0933975011882
1962-01-01	37.8224526424940
1963-01-01	38.3876805454224
1964-01-01	38.7613734919092
1965-01-01	38.9157681797544
1966-01-01	39.0016652681518
1967-01-01	38.8340336412751
1968-01-01	38.4719667717186
1969-01-01	38.0267732761601
1970-01-01	37.5690656198522
1971-01-01	36.8556069306032
1972-01-01	36.2947270829823
1973-01-01	35.8073812514825
1974-01-01	35.2615101694516
1975-01-01	34.6048791969977
1976-01-01	34.1365940794035
1977-01-01	33.5608105251204
1978-01-01	32.9860994560430
1979-01-01	32.5620962001785
1980-01-01	32.3361256748926
1981-01-01	32.0565697928426
1982-01-01	31.9402297749712
1983-01-01	31.9434135781422
1984-01-01	31.9693765332882
1985-01-01	31.9584352500979
1986-01-01	31.8777537408826
1987-01-01	31.8047973607535
1988-01-01	31.7270564190859
1989-01-01	31.6141496439086
1990-01-01	31.4235908532987
1991-01-01	31.3131721690492
1992-01-01	31.0199377918227
1993-01-01	30.6071288943189
1994-01-01	30.1614287931469
1995-01-01	29.7271910194203
1996-01-01	29.2353573002240
1997-01-01	28.8085961065226
1998-01-01	28.4141869597969
1999-01-01	28.0028899664464
2000-01-01	27.5726898527983
2001-01-01	26.8180437316003
2002-01-01	26.1109737452456
2003-01-01	25.4700119646869
2004-01-01	24.9272256523434
2005-01-01	24.5009332136620
2006-01-01	24.2662591938071
2007-01-01	24.0747840067974
2008-01-01	23.9403278859004
2009-01-01	23.9108009478155
2010-01-01	24.0382631208193
2011-01-01	24.4042005408659
2012-01-01	24.8935431745034
2013-01-01	25.5002642199160
2014-01-01	26.1540130396204
2015-01-01	26.7759338100677
2016-01-01	27.4026814714203
2017-01-01	27.9282610304189