Year	Percent
1974	3.62274
1975	9.46166
1976	12.16409
1977	24.24734
1978	18.70577
1979	8.71691
1980	9.17745
1981	18.1261
1982	18.81574
1983	16.48634
1984	23.71385
1985	28.35287
1986	29.27439
1987	16.9199
1988	23.41506
1989	16.20053
1990	12.31147
1991	8.19932
1992	6.22516
1993	7.05057
1994	5.60594
1995	6.14186
1996	9.66038
1997	10.24048
1998	7.36982
1999	8.48598
2000	6.62464
2001	7.53585
2002	2.74219
2003	2.69343
2004	2.78049
2005	2.47872
2006	3.0442
2007	1.58586
2008	16.04653
2009	4.25098
2010	2.6036
2011	0.71731
2012	1.14687
2013	2.25951
2014	2.77071
2015	3.2094