Year	Percent of Total
1960-01-01	37.8218961863992
1961-01-01	38.1236314767115
1962-01-01	38.4630031608210
1963-01-01	38.7864875205365
1964-01-01	39.0072829214203
1965-01-01	39.1069085350906
1966-01-01	39.3431343639861
1967-01-01	39.4731461286805
1968-01-01	39.5008511612627
1969-01-01	39.3765531474400
1970-01-01	39.0202763323165
1971-01-01	39.2221861263782
1972-01-01	39.1903207614881
1973-01-01	38.9832076606374
1974-01-01	38.7772523809877
1975-01-01	38.7315349166689
1976-01-01	38.5425505761438
1977-01-01	38.5175756150756
1978-01-01	38.6387712947625
1979-01-01	38.8776014052243
1980-01-01	39.3091158327622
1981-01-01	39.7366540399833
1982-01-01	40.0678556312948
1983-01-01	40.3825423324589
1984-01-01	40.6778157036967
1985-01-01	40.8845459408854
1986-01-01	41.5710167436121
1987-01-01	42.0631360960394
1988-01-01	42.4133662751102
1989-01-01	42.6968788181717
1990-01-01	42.9513220224624
1991-01-01	42.9579414648317
1992-01-01	43.0055718140034
1993-01-01	43.0292598967298
1994-01-01	42.9352958081866
1995-01-01	42.7004125806394
1996-01-01	42.3506533409415
1997-01-01	41.8841207705697
1998-01-01	41.3974196758977
1999-01-01	40.9704070597249
2000-01-01	40.6217901657597
2001-01-01	40.3568827157599
2002-01-01	40.0717579497214
2003-01-01	39.8346700527346
2004-01-01	39.6614593752630
2005-01-01	39.5324547052291
2006-01-01	39.2887302342666
2007-01-01	39.0329749302748
2008-01-01	38.8170212961961
2009-01-01	38.6283963124415
2010-01-01	38.4326004306574
2011-01-01	38.2881251948627
2012-01-01	38.0641887630670
2013-01-01	37.8394937559170
2014-01-01	37.6341391718256
2015-01-01	37.4248014912510
2016-01-01	37.3520863862987
2017-01-01	37.1952426817619