Year	Percent
1979-01-01	23.0050859599947
1980-01-01	21.9152680172239
1981-01-01	21.2840578649215
1982-01-01	21.9595328659565
1983-01-01	23.3761164480280
1984-01-01	24.2229516508910
1985-01-01	24.4190042049180
1986-01-01	24.0632325130080
1987-01-01	25.1734328261371
1988-01-01	25.3420797814445
1989-01-01	24.5992547486585
1990-01-01	24.7268746327438
1991-01-01	27.4454462818124
1992-01-01	27.7877172236942
1993-01-01	28.3506392213081
1994-01-01	27.0586428468017
1995-01-01	26.3354126006750
1996-01-01	26.2162951282747
1997-01-01	27.4714897075652
1998-01-01	27.9307321247375
1999-01-01	28.1714321437477
2000-01-01	28.1362178829386
2001-01-01	27.7651099682441
2002-01-01	28.3194763807467
2003-01-01	28.5970543965955
2004-01-01	28.8239073677631
2005-01-01	27.9831107102630
2006-01-01	27.9275429342886
2007-01-01	28.2090552333200
2008-01-01	28.0245758827547
2009-01-01	29.5859161164317
2010-01-01	30.3920480551051
2011-01-01	31.2101783763064
2012-01-01	31.7691976187159
2013-01-01	32.6311287628268
2014-01-01	33.1086215058366
2015-01-01	32.1774794120849
2016-01-01	32.8004488636401
2017-01-01	32.6121063590929