Year	Percent
1960	27.32945
1961	24.41823
1962	24.10741
1963	28.29094
1964	29.89786
1965	25.57771
1966	25.56732
1967	25.30033
1968	23.94062
1969	21.52869
1970	23.35223
1971	19.81626
1972	19.38967
1973	16.5515
1974	14.71947
1975	8.6504
1976	11.38806
1977	9.15264
1978	13.65286
1979	19.40136
1980	19.44384
1981	16.07717
1982	8.38117
1983	8.65943
1984	12.69242
1985	13.73852
1986	12.81011
1987	8.2471
1988	7.57267
1989	7.9544
1990	7.24072
1991	7.46443
1992	8.76109
1993	7.06252
1994	8.74053
1995	11.79199
1996	11.96111
1997	13.35951
1998	9.63905
1999	12.25157
2000	10.65141
2001	11.51808
2002	11.21328
2003	11.38672
2004	12.69688
2005	14.1797
2006	15.27541
2007	16.72507
2008	24.28014
2009	17.26798
2010	17.1318
2011	19.01757
2012	20.21672
2013	20.29803
2014	18.17026
2015	18.4443
2016	18.58152
2017	18.5117