Year	Percent
1971	0.74118
1972	4.6683
1973	3.17511
1974	2.5422
1975	4.83715
1976	19.90832
1977	19.91086
1978	18.30191
1979	31.64707
1980	31.69502
1981	31.62457
1982	20.34873
1983	19.8294
1984	21.27975
1985	15.50195
1986	15.08966
1987	16.52548
1988	16.89927
1989	16.94446
1990	17.59602
1991	13.46181
1992	12.75735
1993	13.29254
1994	24.12871
1995	25.15336
1996	25.33838
1997	20.58821
1998	16.20595
1999	15.095
2000	15.68593
2001	14.59335
2002	11.71234
2003	12.89014
2004	13.99926
2005	14.12575
2006	12.88654
2007	9.10986
2008	13.29278
2009	39.24437
2010	29.45176
2011	28.12886
2012	29.39919
2013	34.81332
2014	40.44559
2015	32.30343
2016	35.15053