Year	Percent
1971	13.96753
1972	26.89535
1973	44.2044
1974	55.11929
1975	30.93859
1976	43.60337
1977	27.72159
1978	17.79897
1979	20.14276
1980	20.57907
1981	10.25484
1982	6.32046
1983	10.4318
1984	8.79642
1985	9.70882
1986	8.55863
1987	6.55384
1988	5.25098
1989	6.21072
1990	8.29662
1991	8.63339
1992	8.2841
1993	10.91893
1994	11.06305
1995	10.51525
1996	11.52766
1997	12.0562
1998	9.37698
1999	9.85238
2000	6.8893
2001	6.04999
2002	5.14656
2003	5.85418
2004	7.00276
2005	10.55122
2006	9.97289
2007	16.73082
2008	23.47941
2009	28.40419
2010	17.4302
2011	18.60526
2012	15.15842
2013	23.34126
2014	16.31471
2015	9.12513
2016	12.36832