Year	Percent of Total
1960-01-01	41.6107917997746
1961-01-01	42.0906840859056
1962-01-01	42.6831789312286
1963-01-01	43.2458765327610
1964-01-01	43.5886218301231
1965-01-01	43.6291668498739
1966-01-01	43.5849157273396
1967-01-01	43.2937979488193
1968-01-01	42.8293785637816
1969-01-01	42.3339177695568
1970-01-01	41.8959087903703
1971-01-01	41.4592393209422
1972-01-01	41.0564666792180
1973-01-01	40.6770791547718
1974-01-01	40.2711184434452
1975-01-01	39.8033148399070
1976-01-01	39.6113077740754
1977-01-01	39.4393261354275
1978-01-01	39.2795403984468
1979-01-01	39.1447901801530
1980-01-01	39.0407144225237
1981-01-01	38.5321669106378
1982-01-01	38.0678545866771
1983-01-01	37.6384042195277
1984-01-01	37.2108787426609
1985-01-01	36.7520454250812
1986-01-01	36.3155516046136
1987-01-01	35.8026594834990
1988-01-01	35.2257095052247
1989-01-01	34.6447085020016
1990-01-01	34.1313184975598
1991-01-01	33.5523978169362
1992-01-01	33.0057954641297
1993-01-01	32.5072547601499
1994-01-01	32.0110332678912
1995-01-01	31.4581620455503
1996-01-01	31.0228397634616
1997-01-01	30.4903206614349
1998-01-01	29.8656273011361
1999-01-01	29.2177836855954
2000-01-01	28.6375328169981
2001-01-01	28.7995716486912
2002-01-01	28.8143334477298
2003-01-01	28.7075600357048
2004-01-01	28.4275200238555
2005-01-01	27.9068297493862
2006-01-01	27.1872281168743
2007-01-01	26.2949942566511
2008-01-01	25.2919268497782
2009-01-01	24.3664831051005
2010-01-01	23.7213639123100
2011-01-01	23.6256769291391
2012-01-01	23.7000864859763
2013-01-01	23.8984576113199
2014-01-01	24.0466162759341
2015-01-01	23.9906526196198
2016-01-01	23.5678915498576
2017-01-01	23.0891905884512