Year	Percent
1978-01-01	17.3960188554349
1979-01-01	17.4713768989432
1980-01-01	17.7024915185007
1981-01-01	17.7140852474715
1982-01-01	17.8983660871735
1983-01-01	17.7936632549792
1984-01-01	18.2504090506100
1985-01-01	18.8389315573886
1986-01-01	19.1340031303772
1987-01-01	19.4478381504675
1988-01-01	19.6968609947884
1989-01-01	19.7444735286827
1990-01-01	19.4982612312377
1991-01-01	19.0567790705801
1992-01-01	18.8146313204130
1993-01-01	18.7738069308106
1994-01-01	19.0243980267819
1995-01-01	19.1380829155791
1996-01-01	18.9302922744009
1997-01-01	18.8034194455918
1998-01-01	19.1703094507998
1999-01-01	19.3522397874940
2000-01-01	19.6924584908344
2001-01-01	20.1982598392448
2002-01-01	20.8200934554855
2003-01-01	21.1834658761011
2004-01-01	21.6025864306032
2005-01-01	21.5518945429416
2006-01-01	21.3699178162576
2007-01-01	21.1019187206864
2008-01-01	21.1776409320937
2009-01-01	21.7056182514667
2010-01-01	21.8036297331698
2011-01-01	22.0502711478478
2012-01-01	22.3042875386673
2013-01-01	22.2137757576033
2014-01-01	22.1440903679028
2015-01-01	21.9672668451695
2016-01-01	21.5042293086347
2017-01-01	21.2543836291243