Year	Percent of Total
1960-01-01	28.0872066966822
1961-01-01	28.2480360536062
1962-01-01	28.2957878769971
1963-01-01	28.2483485537914
1964-01-01	28.1504518971074
1965-01-01	28.0225127918888
1966-01-01	27.8933219699969
1967-01-01	27.7173931806754
1968-01-01	27.5035146153842
1969-01-01	27.2623212848988
1970-01-01	27.0067194123589
1971-01-01	26.7008782408858
1972-01-01	26.4085034322120
1973-01-01	26.1211211882715
1974-01-01	25.8203233673710
1975-01-01	25.4997231338633
1976-01-01	25.2389332514246
1977-01-01	24.9376351604065
1978-01-01	24.6193296325925
1979-01-01	24.3204131300381
1980-01-01	24.0608570578449
1981-01-01	23.8516392949738
1982-01-01	23.6882075421160
1983-01-01	23.5574436406724
1984-01-01	23.4331839582104
1985-01-01	23.3007024164060
1986-01-01	23.2048655013896
1987-01-01	23.0939258420046
1988-01-01	22.9645918272436
1989-01-01	22.8149824389768
1990-01-01	22.6378173521910
1991-01-01	22.4932363509613
1992-01-01	22.2962161602539
1993-01-01	22.0611496144283
1994-01-01	21.8078200955206
1995-01-01	21.5427878073699
1996-01-01	21.1957949257556
1997-01-01	20.8710163895212
1998-01-01	20.5468139920570
1999-01-01	20.1954679047608
2000-01-01	19.8183395767273
2001-01-01	19.4532210752094
2002-01-01	19.0672699004451
2003-01-01	18.6821743174369
2004-01-01	18.3360884265384
2005-01-01	18.0499562353955
2006-01-01	17.8390994335917
2007-01-01	17.6734216600540
2008-01-01	17.5547540888793
2009-01-01	17.4756154425388
2010-01-01	17.4301713625701
2011-01-01	17.4667098504198
2012-01-01	17.5101138005123
2013-01-01	17.5716514790649
2014-01-01	17.6485599843674
2015-01-01	17.7299697004384
2016-01-01	17.7960685888284
2017-01-01	17.8561166591158