Year	Percent of Total
1960-01-01	30.9198436630748
1961-01-01	30.9162146042004
1962-01-01	30.9273303437798
1963-01-01	30.9309743603129
1964-01-01	30.9175230214867
1965-01-01	30.8895070027326
1966-01-01	30.8830457185773
1967-01-01	30.7748277773406
1968-01-01	30.6482278365786
1969-01-01	30.6245012852335
1970-01-01	30.7539530535275
1971-01-01	30.6084506306618
1972-01-01	30.7155007845512
1973-01-01	30.9335740810802
1974-01-01	31.0707322331074
1975-01-01	31.0444373118400
1976-01-01	31.1888705007484
1977-01-01	31.0670369503854
1978-01-01	30.7966715193798
1979-01-01	30.5538421620602
1980-01-01	30.4118862761732
1981-01-01	30.2490607241005
1982-01-01	30.2273375630463
1983-01-01	30.2546084462888
1984-01-01	30.1854854104595
1985-01-01	29.9481985627324
1986-01-01	29.6620097856662
1987-01-01	29.2274956884001
1988-01-01	28.6702126467312
1989-01-01	28.0791099347432
1990-01-01	27.5148301173045
1991-01-01	26.7685575477963
1992-01-01	26.1077179530479
1993-01-01	25.4933001263290
1994-01-01	24.8767852864192
1995-01-01	24.2492424439518
1996-01-01	23.5652060723144
1997-01-01	22.9214882622431
1998-01-01	22.3259664530991
1999-01-01	21.8039154316504
2000-01-01	21.3707942473140
2001-01-01	20.9821571317371
2002-01-01	20.6467690469101
2003-01-01	20.3846998195107
2004-01-01	20.2173830378161
2005-01-01	20.1525667004591
2006-01-01	20.1614316221938
2007-01-01	20.2502095804231
2008-01-01	20.4051640361735
2009-01-01	20.5734858355750
2010-01-01	20.7058549430637
2011-01-01	20.9995369515455
2012-01-01	21.2488486286256
2013-01-01	21.4457940434010
2014-01-01	21.6047168508862
2015-01-01	21.7352073048550
2016-01-01	21.7035986287150
2017-01-01	21.6376568072837