Year	Percent
1960	30.26804
1961	29.24386
1962	31.62816
1963	37.40102
1964	41.38981
1965	35.73592
1966	41.58981
1967	44.69379
1968	39.36768
1969	38.9322
1970	34.13393
1971	32.34269
1972	31.83135
1973	32.78745
1974	33.48356
1975	30.64881
1976	25.76734
1977	28.54223
1978	21.01676
1979	21.30104
1980	24.7162
1981	25.04305
1982	30.73583
1983	23.83557
1984	27.12361
1985	23.70354
1986	20.76158
1987	27.81035
1988	26.16809
1989	23.01589
1990	19.01838
1991	15.82721
1992	17.84807
1993	18.37687
1994	34.07058
1995	31.02055
1996	28.57735
1997	32.41832
1998	30.7028
1999	27.71448
2000	30.39912
2001	26.72152
2002	26.93194
2003	21.58359
2004	22.4453
2005	22.65654
2006	24.65586
2007	25.13559
2008	22.66727
2009	19.67975
2010	22.15491
2011	22.77282
2012	24.27045
2013	21.6733
2014	29.59834
2015	27.26521
2016	23.56373
2017	24.3863