Year	Percent
1960	25.74758
1961	27.82821
1962	29.54496
1963	30.86295
1964	31.40206
1965	32.82713
1966	33.56323
1967	35.1855
1968	36.30295
1969	38.53898
1970	40.58258
1971	43.13484
1972	43.3949
1973	53.64564
1974	62.32333
1975	56.73269
1976	57.24302
1977	53.29132
1978	45.68279
1979	45.75337
1980	35.1536
1981	34.72087
1982	40.53819
1983	38.05908
1984	34.43982
1985	30.55545
1986	24.90974
1987	24.97876
1988	24.80721
1989	26.14509
1990	32.79982
1991	33.3941
1992	33.54157
1993	42.02935
1994	43.37016
1995	39.44042
1996	42.08254
1997	38.71144
1998	32.50355
1999	37.45889
2000	40.30591
2001	39.91726
2002	45.50293
2003	45.05995
2004	47.47047
2005	49.63725
2006	48.2599
2007	48.23566
2008	47.66879
2009	43.09652
2010	44.20938
2011	47.92205
2012	43.34185
2013	42.88103
2014	39.62276
2015	32.96959
2016	33.86012
2017	21.21598