Year	Percent
1978	0.3784
1979	0.2698
1980	0.3393
1981	0.3284
1982	0.6102
1983	0.9365
1984	0.9236
1985	1.0532
1986	1.0672
1987	0.7496
1988	0.6853
1989	0.6645
1990	0.7428
1991	0.7194
1992	0.8959
1993	0.7832
1994	0.8699
1995	0.9966
1996	1.5112
1997	1.5162
1998	1.4421
1999	1.5764
2000	1.6672
2001	2.6615
2002	3.0513
2003	3.2877
2004	3.1149
2005	3.051
2006	3.0052
2007	3.0303
2008	3.0955
2009	4.213
2010	3.7875
2011	3.3124
2012	3.2114
2013	3.0788
2014	2.9455
2015	2.9046
2016	2.954
2017	2.8275