Year	Percent
1960	44.27278
1961	41.92073
1962	40.43478
1963	40.04545
1964	40.1324
1965	41.2189
1966	48.56809
1967	50.31494
1968	50.54397
1969	50.4819
1970	46.32814
1971	48.18031
1972	46.14047
1973	49.14838
1974	53.18774
1975	32.15054
1976	34.22354
1977	36.46646
1978	33.27668
1979	33.79949
1980	32.80916
1981	32.33789
1982	29.42141
1983	27.36532
1984	28.03911
1985	26.97967
1986	25.98765
1987	23.27907
1988	25.92816
1989	25.17511
1990	22.48262
1991	18.06826
1992	16.79025
1993	16.13965
1994	27.30354
1995	29.54994
1996	26.17664
1997	27.00737
1998	24.98677
1999	21.82494
2000	22.90421
2001	19.6207
2002	28.56148
2003	27.90153
2004	32.46827
2005	33.83673
2006	37.1496
2007	37.22863
2008	40.2351
2009	34.46136
2010	35.34562
2011	35.27539
2012	35.40221
2013	32.40681
2014	30.24748
2015	25.38354
2016	29.92654
2017	31.65676