Year	Percent
1968-01-01	57.2274091344634
1969-01-01	56.0575299136026
1970-01-01	56.5379594247428
1971-01-01	57.8620476429148
1972-01-01	56.2433778251594
1973-01-01	54.0930973184214
1974-01-01	51.6461709793959
1975-01-01	48.5017057193839
1976-01-01	46.6363773258814
1977-01-01	44.0755390984469
1978-01-01	43.0588193232789
1979-01-01	42.2117135231686
1980-01-01	41.3103857358052
1981-01-01	41.6451656672826
1982-01-01	41.4784567589350
1983-01-01	42.0291196483457
1984-01-01	41.3190671894346
1985-01-01	40.6601595999533
1986-01-01	40.5478040654045
1987-01-01	40.0884794491797
1988-01-01	40.1158263523412
1989-01-01	40.5289218088572
1990-01-01	41.6729454371215
1991-01-01	43.2171280415072
1992-01-01	44.5910159877377
1993-01-01	45.3098412323955
1994-01-01	45.3828300926377
1995-01-01	45.0933614972441
1996-01-01	45.7274510926909
1997-01-01	46.0960587721734
1998-01-01	44.8735117273158
1999-01-01	43.0053744539927
2000-01-01	42.5889999049320
2001-01-01	41.6740314477352
2002-01-01	40.9484895738790
2003-01-01	40.0564248373092
2004-01-01	39.4476583390716
2005-01-01	40.0892001252792
2006-01-01	40.6446994533888
2007-01-01	41.2813684348673
2008-01-01	40.8288203829318
2009-01-01	38.2423533641051
2010-01-01	37.4737333673164
2011-01-01	37.9853844439514
2012-01-01	37.7962234469428
2013-01-01	38.5640613038593
2014-01-01	39.3013508031425
2015-01-01	39.9379779311083
2016-01-01	41.7776555856446
2017-01-01	42.0912591752383