Year	Percent
1971	7.94497
1972	17.28801
1973	25.65192
1974	13.88007
1975	20.42158
1976	15.94197
1977	17.02412
1978	25.5472
1979	31.2987
1980	23.56913
1981	17.44338
1982	21.17849
1983	17.48351
1984	22.27179
1985	24.4666
1986	22.55147
1987	10.00985
1988	9.91176
1989	12.81227
1990	7.97009
1991	14.70954
1992	9.12932
1993	10.57947
1994	12.60284
1995	13.54195
1996	14.43847
1997	9.73055
1998	6.55322
1999	7.52783
2000	4.58082
2001	5.47933
2002	8.32507
2003	17.70943
2004	24.16845
2005	25.86603
2006	61.36159
2007	44.00292
2008	36.87821
2009	49.99082
2010	56.59541
2011	52.68473
2012	45.45449
2013	33.60778
2014	30.30103
2015	27.83522
2016	27.41967