Year	Percent of Total
1960-01-01	37.3565132725223
1961-01-01	37.4329891789933
1962-01-01	37.5567785815569
1963-01-01	37.7079331820034
1964-01-01	37.8340238657018
1965-01-01	37.8991228070175
1966-01-01	37.9501739854407
1967-01-01	37.9281989362034
1968-01-01	37.8535427800708
1969-01-01	37.8045660303090
1970-01-01	37.8242375906726
1971-01-01	38.0305927342256
1972-01-01	38.2479301468030
1973-01-01	38.3984323103494
1974-01-01	38.3709269193423
1975-01-01	38.1095314131303
1976-01-01	38.3860893933861
1977-01-01	38.3051932463791
1978-01-01	38.0144726054254
1979-01-01	37.7178481367330
1980-01-01	37.4841536680814
1981-01-01	37.0701760336465
1982-01-01	36.8587857715967
1983-01-01	36.6779862187201
1984-01-01	36.3139754178318
1985-01-01	35.7009142080496
1986-01-01	35.1215629796669
1987-01-01	34.3166156678359
1988-01-01	33.3910352083384
1989-01-01	32.5425765175863
1990-01-01	31.8764098547003
1991-01-01	31.2240616065665
1992-01-01	30.7669342346148
1993-01-01	30.4573078509556
1994-01-01	30.1877979641799
1995-01-01	29.9074093492440
1996-01-01	29.8136423243996
1997-01-01	29.6332273489723
1998-01-01	29.4132628073269
1999-01-01	29.2033828422395
2000-01-01	29.0124065748740
2001-01-01	28.7463140434943
2002-01-01	28.5067484440585
2003-01-01	28.2469581292828
2004-01-01	27.9120773495629
2005-01-01	27.4851086872438
2006-01-01	26.8475479518684
2007-01-01	26.1501109820138
2008-01-01	25.4239373877089
2009-01-01	24.7270757801732
2010-01-01	24.1072033206260
2011-01-01	23.7652999917536
2012-01-01	23.4916271416126
2013-01-01	23.2690185536621
2014-01-01	23.0567577034769
2015-01-01	22.8320530972794
2016-01-01	22.6975505818239
2017-01-01	22.5186874445711