Year	Percent
1971	7.79594
1972	11.36313
1973	16.96239
1974	14.5404
1975	16.07725
1976	31.31172
1977	38.84936
1978	53.14575
1979	83.04599
1980	90.7248
1981	68.10354
1982	53.28333
1983	30.17313
1984	14.54698
1985	15.18068
1986	22.33905
1987	19.8193
1988	21.49302
1989	22.61955
1990	27.97328
1991	39.36683
1992	45.31297
1993	42.12251
1994	36.66707
1995	33.53445
1996	34.20173
1997	30.82338
1998	26.30095
1999	23.3009
2000	26.27744
2001	28.01315
2002	32.3387
2003	29.29735
2004	35.44578
2005	39.9158
2006	40.29476
2007	47.65538
2008	50.69915
2009	46.85357
2010	43.80272
2011	43.21128
2012	48.18582
2013	48.10365
2014	46.17419
2015	41.68904
2016	38.38792