Year	Percent
1960	15.26366
1961	14.3402
1962	14.53453
1963	25.19829
1964	43.53881
1965	42.195
1966	42.99816
1967	41.60739
1968	38.00216
1969	38.84045
1970	40.81239
1971	40.22034
1972	48.22487
1973	46.8333
1974	48.29592
1975	38.44037
1976	37.94484
1977	32.78007
1978	33.36672
1979	33.18556
1980	36.82315
1981	45.06646
1982	40.06448
1983	45.73719
1984	45.58725
1985	59.90894
1986	56.15325
1987	49.0893
1988	50.26847
1989	49.8324
1990	45.64191
1991	34.74317
1992	28.22277
1993	31.99343
1994	43.77442
1995	52.33618
1996	49.40559
1997	42.12489
1998	30.85583
1999	27.23883
2000	29.96142
2001	29.39752
2002	28.33827
2003	21.44962
2004	25.64942
2005	30.72417
2006	46.69952
2007	44.87296
2008	45.94791
2009	40.94228
2010	50.7447
2011	56.13291
2012	53.02395
2013	49.82639
2014	39.14783
2015	37.1046
2016	37.15047
2017	43.18115