Year	Percent
1979-01-01	3.20616781667938
1980-01-01	2.87309334840718
1981-01-01	3.15294426337887
1982-01-01	3.55143553943318
1983-01-01	5.91467046766548
1984-01-01	5.58840751350023
1985-01-01	6.16574068426095
1986-01-01	5.44883190871873
1987-01-01	5.83816281979017
1988-01-01	5.88916281004364
1989-01-01	5.29485698792373
1990-01-01	5.45892265063963
1991-01-01	7.94946794212280
1992-01-01	9.50655370808476
1993-01-01	11.00927749622350
1994-01-01	9.68407758718006
1995-01-01	7.63144104986666
1996-01-01	7.58604727168381
1997-01-01	6.77623729119563
1998-01-01	6.29874742554424
1999-01-01	5.49879276886891
2000-01-01	4.54710899428949
2001-01-01	4.57579181082419
2002-01-01	4.30195731597010
2003-01-01	3.77768314783815
2004-01-01	3.55418850407294
2005-01-01	3.37978506051833
2006-01-01	3.22960347795049
2007-01-01	2.74003600463797
2008-01-01	2.60984624041412
2009-01-01	3.34211255564421
2010-01-01	3.25551491199804
2011-01-01	3.32824107365530
2012-01-01	3.45363607258485
2013-01-01	3.82858998001507
2014-01-01	4.09037498242339
2015-01-01	4.25384175336590
2016-01-01	4.25408616714113
2017-01-01	4.07196031722021