Year	Percent
1970	3.99993
1971	4.15811
1972	4.35557
1973	6.05984
1974	5.01837
1975	5.18491
1976	5.27258
1977	9.30433
1978	7.73469
1979	7.27221
1980	12.68756
1981	11.19316
1982	7.84024
1983	6.00915
1984	13.40121
1985	9.75799
1986	5.23522
1987	11.367
1988	12.4409
1989	8.89072
1990	9.93599
1991	9.98249
1992	4.90249
1993	8.86944
1994	16.45441
1995	11.66717
1996	10.5244
1997	21.01676
1998	14.4437
1999	24.86118
2000	21.75586
2001	21.1946
2002	17.83312
2003	18.67981
2004	18.45989
2005	16.14973
2006	12.84867
2007	20.19104
2008	19.85061
2009	18.84934
2010	14.90608
2011	25.67401
2012	15.47521
2013	18.25719
2014	20.2074
2015	27.54304
2016	26.50811
2017	27.361