Year	Percent
1960	26.16902
1961	24.55333
1962	28.90352
1963	30.24251
1964	30.49999
1965	32.40708
1966	34.12061
1967	35.04413
1968	30.3923
1969	27.18018
1970	29.19189
1971	28.53958
1972	29.64206
1973	37.80274
1974	42.60729
1975	36.93973
1976	31.84204
1977	37.42649
1978	31.24929
1979	28.13236
1980	43.26836
1981	41.781
1982	26.05523
1983	29.99262
1984	29.45081
1985	21.82626
1986	20.8316
1987	13.76037
1988	58.27021
1989	65.19167
1990	46.34245
1991	52.50599
1992	53.2664
1993	47.85804
1994	25.94134
1995	27.94471
1996	31.63548
1997	38.58599
1998	37.67927
1999	44.00737
2000	41.19033
2001	38.93822
2002	39.24415
2003	41.47007
2004	44.13546
2005	47.26359
2006	56.04304
2007	59.96216
2008	62.32352
2009	53.01212
2010	59.89694
2011	66.81048
2012	67.70811
2013	65.76994
2014	61.69013
2015	58.92201
2016	55.99314
2017	55.42403