Year	Percent
1968-01-01	41.6828752336610
1969-01-01	42.7864873931598
1970-01-01	42.3123543669009
1971-01-01	40.8182835447717
1972-01-01	42.1679925804819
1973-01-01	44.5327032374860
1974-01-01	46.9764435344096
1975-01-01	49.7591217487076
1976-01-01	51.6292229423608
1977-01-01	54.0320998895903
1978-01-01	55.0093600809313
1979-01-01	56.0993959215053
1980-01-01	57.0107302511685
1981-01-01	56.5694161594565
1982-01-01	56.6066879151517
1983-01-01	55.9139918290200
1984-01-01	56.5701609472790
1985-01-01	57.3303248978978
1986-01-01	57.1994717755463
1987-01-01	57.5909826988882
1988-01-01	57.7721448071659
1989-01-01	57.4652557990643
1990-01-01	56.3340143542631
1991-01-01	54.6602978063040
1992-01-01	53.2107572945383
1993-01-01	52.3359389354124
1994-01-01	51.8767745317938
1995-01-01	51.9133340074057
1996-01-01	50.9812407196801
1997-01-01	50.5289561269352
1998-01-01	51.0765759898499
1999-01-01	52.1620347203780
2000-01-01	52.5659946988600
2001-01-01	53.3965255596930
2002-01-01	53.9192911651318
2003-01-01	54.7222664082128
2004-01-01	55.7784173848223
2005-01-01	55.5278813563407
2006-01-01	55.3529772821270
2007-01-01	55.0063491439491
2008-01-01	55.6851920234538
2009-01-01	57.4332929830870
2010-01-01	58.0038999565148
2011-01-01	58.0096452723727
2012-01-01	58.5058353033552
2013-01-01	58.3149608357352
2014-01-01	57.8295429414053
2015-01-01	57.5918658660998
2016-01-01	55.6400341033589
2017-01-01	55.7444526348312