Year	Percent
1979-01-01	3.75278250591511
1980-01-01	3.67713398916766
1981-01-01	3.67345107787707
1982-01-01	4.69669737292982
1983-01-01	6.95112872234704
1984-01-01	6.25827346152604
1985-01-01	5.88615614977758
1986-01-01	5.73202385761174
1987-01-01	5.87194423431174
1988-01-01	5.26151665296969
1989-01-01	4.62132353508020
1990-01-01	5.06726911421688
1991-01-01	7.28688166585754
1992-01-01	8.29859552875602
1993-01-01	8.75308150153995
1994-01-01	7.74270472115431
1995-01-01	6.64669213851354
1996-01-01	6.62426618929629
1997-01-01	6.49606712933871
1998-01-01	6.03071339311726
1999-01-01	5.38136448663894
2000-01-01	4.91584020346756
2001-01-01	5.14743297925359
2002-01-01	4.86823603417618
2003-01-01	4.51702774080658
2004-01-01	3.99530163764028
2005-01-01	3.72894785252990
2006-01-01	3.56689599122998
2007-01-01	3.22898713315444
2008-01-01	3.18062929933212
2009-01-01	4.24157960240127
2010-01-01	3.82951361906198
2011-01-01	3.73675776059617
2012-01-01	3.85871226708017
2013-01-01	4.31272938205082
2014-01-01	4.60613811476549
2015-01-01	4.62701418731149
2016-01-01	4.33010547227149
2017-01-01	4.21688066569612