Year	Percent
1968-01-01	54.8504127551188
1969-01-01	54.0302796768466
1970-01-01	54.5388439100322
1971-01-01	54.9147970863073
1972-01-01	52.9797224085995
1973-01-01	51.6348086378528
1974-01-01	48.8542953588040
1975-01-01	46.5397687587107
1976-01-01	44.8944748897937
1977-01-01	43.7831827214508
1978-01-01	43.1402534957795
1979-01-01	42.5262033471831
1980-01-01	41.9333725636887
1981-01-01	41.9644261869724
1982-01-01	41.5924051413495
1983-01-01	42.3034300771180
1984-01-01	41.7371800514273
1985-01-01	40.9912984543158
1986-01-01	41.0662103034009
1987-01-01	40.5631239877789
1988-01-01	40.6876979510066
1989-01-01	41.3796418299538
1990-01-01	42.3745471453184
1991-01-01	43.6141253966432
1992-01-01	44.6291461327124
1993-01-01	44.8181558010168
1994-01-01	45.0663237450404
1995-01-01	44.7767169441504
1996-01-01	45.1632355981373
1997-01-01	45.3636210238519
1998-01-01	44.5978304614909
1999-01-01	43.0246190295413
2000-01-01	42.8306449028890
2001-01-01	42.0581629362289
2002-01-01	41.0221351679720
2003-01-01	40.3586990302645
2004-01-01	40.0905010213504
2005-01-01	40.9096376197889
2006-01-01	41.3281827803171
2007-01-01	41.3905111730870
2008-01-01	41.2324286889580
2009-01-01	39.5404856070610
2010-01-01	38.7914169490452
2011-01-01	39.0609467658239
2012-01-01	38.3360959981115
2013-01-01	39.5089902186604
2014-01-01	40.0433058345888
2015-01-01	40.2989627892585
2016-01-01	42.1801285771497
2017-01-01	42.5633804134354