Year	Percent
1960	10.68332
1961	14.58431
1962	15.02703
1963	13.39001
1964	13.3223
1976	19.74878
1977	15.56756
1978	13.77029
1979	14.24064
1980	14.66297
1981	19.31147
1982	18.86123
1983	14.75437
1984	8.54078
1985	9.4923
1986	14.36951
1987	15.08682
1988	4.32924
1989	5.19014
1990	11.19658
1991	16.11124
1992	19.0474
1993	21.70873
1994	17.39043
1995	14.12363
1996	12.47306
1997	15.77055
1998	17.94907
1999	16.81063
2000	24.88803
2001	24.47666
2002	26.42305
2003	26.71466
2004	29.32061
2005	28.12863
2006	28.92233
2007	27.5919
2008	24.57527
2009	24.49589
2010	23.04572
2011	21.57811
2012	19.13909
2013	19.53195
2014	16.43966
2015	16.56004
2016	19.61238
2017	18.89119