Year	Percent of Total
1960-01-01	43.5443230782928
1961-01-01	43.8898840078390
1962-01-01	44.1640512888060
1963-01-01	44.4081875380014
1964-01-01	44.6980777314453
1965-01-01	45.0889087885378
1966-01-01	45.5839994438326
1967-01-01	45.8856667864519
1968-01-01	46.0600583724719
1969-01-01	46.1168579754432
1970-01-01	46.0237952706158
1971-01-01	46.4584676783248
1972-01-01	46.8440060514115
1973-01-01	47.1431816803435
1974-01-01	47.3125192971185
1975-01-01	47.3431808729188
1976-01-01	48.1574420455183
1977-01-01	48.6265328208039
1978-01-01	48.8414450231228
1979-01-01	48.9333400010001
1980-01-01	48.9844686412104
1981-01-01	48.5662847245218
1982-01-01	48.2440643852174
1983-01-01	47.9434445373331
1984-01-01	47.5738627290475
1985-01-01	47.1272813913056
1986-01-01	46.9604821837745
1987-01-01	46.6545627649327
1988-01-01	46.3028550065915
1989-01-01	46.0033702275360
1990-01-01	45.7661977732854
1991-01-01	44.6074300513690
1992-01-01	43.6030157769345
1993-01-01	42.6645289061928
1994-01-01	41.6943493253909
1995-01-01	40.6668497742354
1996-01-01	40.5296188405794
1997-01-01	40.3140596328804
1998-01-01	40.0436330843570
1999-01-01	39.7550778191146
2000-01-01	39.4585675849919
2001-01-01	39.1465687182511
2002-01-01	38.7801163804060
2003-01-01	38.3894341323168
2004-01-01	38.0324788934162
2005-01-01	37.7730149099309
2006-01-01	37.5493576927899
2007-01-01	37.3708642281499
2008-01-01	37.2359981521835
2009-01-01	37.1188820128554
2010-01-01	37.0035879421752
2011-01-01	36.8987859050557
2012-01-01	36.7539339334154
2013-01-01	36.5726055284720
2014-01-01	36.3405584957544
2015-01-01	36.0273959740600
2016-01-01	35.7807090292288
2017-01-01	35.5047584848748