Year	Percent
1960	54.76825
1961	50.25407
1962	48.01932
1963	49.40909
1964	46.91767
1965	49.65741
1966	59.05903
1967	59.00731
1968	57.68359
1969	62.00471
1970	60.26704
1971	63.56919
1972	60.93533
1973	60.10481
1974	74.87792
1975	63.22581
1976	61.1276
1977	55.14821
1978	55.33651
1979	58.55683
1980	68.81369
1981	58.71436
1982	51.84942
1983	43.88298
1984	43.36053
1985	36.74206
1986	32.60382
1987	31.06598
1988	29.31346
1989	37.69815
1990	42.04739
1991	35.00112
1992	28.6637
1993	20.41292
1994	22.93766
1995	22.85021
1996	23.34945
1997	25.19219
1998	31.1095
1999	27.232
2000	19.72877
2001	23.57149
2002	18.79088
2003	19.74462
2004	26.10572
2005	30.42223
2006	65.01649
2007	54.1248
2008	56.90864
2009	44.12484
2010	52.54732
2011	64.39466
2012	57.74005
2013	50.42695
2014	44.95779
2015	38.4634
2016	49.78452
2017	68.92978