Year	Percent
1971	33.33366
1972	18.16357
1973	20.17895
1974	16.358
1975	9.84702
1976	6.0891
1977	4.02491
1978	3.74382
1979	6.28528
1980	6.33718
1981	3.94536
1982	4.29593
1983	3.66601
1984	1.46148
1985	4.48149
1986	1.26919
1987	1.70924
1988	2.08182
1989	1.87754
1990	2.9141
1991	2.76508
1993	2.96895
1994	3.93812
1995	3.20075
1996	3.15449
1997	3.58996
1998	1.00987
1999	0.76313
2000	4.21277
2001	2.9637
2002	8.01737
2003	3.60369
2004	4.47077
2005	10.25103
2006	30.29594
2007	38.14819
2008	35.57566
2009	50.12981
2010	47.75655
2011	45.57654
2012	51.94152
2013	45.60552
2014	40.91301
2015	33.94511
2016	24.64149