Year	Percent
1960	34.23955
1961	35.29252
1962	34.39262
1963	33.93545
1964	35.88603
1965	36.82341
1966	36.40699
1967	36.22372
1968	40.69987
1969	36.7618
1970	35.76933
1971	32.20999
1972	33.51212
1973	35.75389
1974	45.69689
1975	36.72858
1976	41.74147
1977	42.62604
1978	36.5212
1979	34.60332
1980	35.00163
1981	35.175
1982	36.42323
1983	36.95986
1984	45.31193
1985	46.77491
1986	39.49591
1987	33.42999
1988	30.48813
1989	32.03334
1990	31.68987
1991	30.01173
1992	31.90949
1993	29.44245
1994	40.5274
1995	41.7593
1996	41.101
1997	42.91596
1998	41.3964
1999	42.40238
2000	40.78103
2001	40.70006
2002	47.46235
2003	41.89142
2004	46.40501
2005	49.89836
2006	52.36759
2007	47.22598
2008	47.11609
2009	50.85444
2010	50.63264
2011	53.81996
2012	48.47613
2013	41.53105
2014	36.65883
2015	35.40638
2016	29.359
2017	29.18124