Year	Percent of Total
1960-01-01	34.8911112123559
1961-01-01	35.0529905180737
1962-01-01	35.0619284005889
1963-01-01	34.9482065719628
1964-01-01	34.7611150429391
1965-01-01	34.5197672544238
1966-01-01	34.2535514641776
1967-01-01	33.9243468878070
1968-01-01	33.5350004257045
1969-01-01	33.0993098121540
1970-01-01	32.6401729721268
1971-01-01	32.0936027196168
1972-01-01	31.5987786346812
1973-01-01	31.1201330739519
1974-01-01	30.6133241790103
1975-01-01	30.0518182235062
1976-01-01	29.5944909233695
1977-01-01	29.0579755788110
1978-01-01	28.4813740798572
1979-01-01	27.9492089888237
1980-01-01	27.5087399567164
1981-01-01	27.1407761939445
1982-01-01	26.8642640042183
1983-01-01	26.6512441794940
1984-01-01	26.4383940236508
1985-01-01	26.1960742108270
1986-01-01	25.9660051323819
1987-01-01	25.7002460980506
1988-01-01	25.4168068034402
1989-01-01	25.1579752231462
1990-01-01	24.9444211368279
1991-01-01	24.7950501506071
1992-01-01	24.7144927369105
1993-01-01	24.6577272173489
1994-01-01	24.5653207009180
1995-01-01	24.4114053409758
1996-01-01	24.3039052378308
1997-01-01	24.0545783234143
1998-01-01	23.7304573985819
1999-01-01	23.4321805160687
2000-01-01	23.2039510046891
2001-01-01	22.8750083949849
2002-01-01	22.6952044832457
2003-01-01	22.5739012057565
2004-01-01	22.4102039133780
2005-01-01	22.1798839917418
2006-01-01	21.9278812790263
2007-01-01	21.6326998689384
2008-01-01	21.3288557790044
2009-01-01	21.0509165227185
2010-01-01	20.7974326315527
2011-01-01	20.7394146275099
2012-01-01	20.6287669802105
2013-01-01	20.5003226013595
2014-01-01	20.3897594524735
2015-01-01	20.3129210914387
2016-01-01	20.1672912769119
2017-01-01	20.0916349526155