Year	Percent of Total
1960-01-01	38.6548353360511
1961-01-01	39.7829297174182
1962-01-01	40.6608822179957
1963-01-01	41.2938642407615
1964-01-01	41.7009246628668
1965-01-01	41.8780490893206
1966-01-01	41.7885784508208
1967-01-01	41.4332459501933
1968-01-01	40.8550938304305
1969-01-01	40.1352456936366
1970-01-01	39.3376804161477
1971-01-01	38.2249374542549
1972-01-01	37.2224091901705
1973-01-01	36.2775321708608
1974-01-01	35.3030034822931
1975-01-01	34.2705357360338
1976-01-01	33.4165980580562
1977-01-01	32.4739104578589
1978-01-01	31.5542980258630
1979-01-01	30.8023501978449
1980-01-01	30.2702055745768
1981-01-01	29.9319397273015
1982-01-01	29.8052469779434
1983-01-01	29.8192363723270
1984-01-01	29.8641798517468
1985-01-01	29.8846650189527
1986-01-01	29.9240092728851
1987-01-01	29.9680585595007
1988-01-01	30.0237027880950
1989-01-01	30.0691735174266
1990-01-01	30.0438786772239
1991-01-01	30.0268368798697
1992-01-01	29.9338621649176
1993-01-01	29.7622906022959
1994-01-01	29.5301279669637
1995-01-01	29.2573497004670
1996-01-01	28.7169904820222
1997-01-01	28.0994521056875
1998-01-01	27.4021740389181
1999-01-01	26.6314170495015
2000-01-01	25.8111186256918
2001-01-01	24.8087377956537
2002-01-01	23.8759259131078
2003-01-01	23.0107568213464
2004-01-01	22.2058700025195
2005-01-01	21.4615368876035
2006-01-01	20.9301673145175
2007-01-01	20.4171689868860
2008-01-01	19.9634828176685
2009-01-01	19.6332528325297
2010-01-01	19.4607395585670
2011-01-01	19.4278651862006
2012-01-01	19.4611096344731
2013-01-01	19.5633053154492
2014-01-01	19.7027066085843
2015-01-01	19.8445636709577
2016-01-01	19.9201932702775
2017-01-01	20.0066542681158