Year	Percent
1974	2.70592
1975	3.49219
1976	3.42187
1977	3.20609
1978	3.16319
1979	3.02026
1980	2.91722
1981	2.88462
1982	2.90193
1983	2.39813
1984	2.28542
1985	2.1706
1986	2.00977
1987	1.72219
1988	1.53084
1989	1.38914
1990	1.41049
1991	1.32406
1992	1.35688
1993	1.22356
1994	1.26616
1995	1.22631
1996	1.26439
1997	1.49774
1998	1.01912
1999	0.81081
2000	0.68448
2001	0.57279
2002	0.70012
2003	0.90929
2004	0.94571
2005	0.75079
2006	0.71642
2007	0.77479
2008	0.63348
2009	0.61241
2010	0.61759
2011	0.65378
2012	0.71155
2013	0.91877
2014	0.77814
2015	0.88627
2016	0.79069
2017	0.80934