Year	Percent
1978-01-01	34.3012172381028
1979-01-01	34.1243175545282
1980-01-01	34.1610104274441
1981-01-01	34.1254587797006
1982-01-01	33.9591975890851
1983-01-01	33.2933063588672
1984-01-01	33.4688575633548
1985-01-01	33.7355304667982
1986-01-01	33.8490534612298
1987-01-01	33.9194613862885
1988-01-01	33.8575015495241
1989-01-01	33.4664529324644
1990-01-01	32.9503967589849
1991-01-01	32.3622056165083
1992-01-01	32.2260256308867
1993-01-01	32.4095081701401
1994-01-01	32.5711750804299
1995-01-01	32.6472202447917
1996-01-01	32.4175302074177
1997-01-01	32.0444343203984
1998-01-01	32.2476016290504
1999-01-01	32.4999827970423
2000-01-01	32.7408550048670
2001-01-01	32.9331305110559
2002-01-01	33.4567007463646
2003-01-01	33.6218515501346
2004-01-01	33.7302236001031
2005-01-01	33.4838115781708
2006-01-01	33.2001834321358
2007-01-01	32.8869119623775
2008-01-01	32.8086716353179
2009-01-01	32.8323400070548
2010-01-01	32.7527430491686
2011-01-01	32.9105908072936
2012-01-01	32.9200178386416
2013-01-01	32.2723325263002
2014-01-01	31.8915876208596
2015-01-01	31.4839180287794
2016-01-01	30.6621804051641
2017-01-01	29.9021845572973