Year	Percent
1964	29.07699
1965	28.86638
1966	27.77778
1967	27.07838
1968	23.68278
1969	27.62974
1970	31.02137
1971	31.26783
1972	27.77265
1973	24.6388
1974	24.09686
1975	25.1085
1976	21.54001
1977	19.71951
1978	19.82263
1979	19.9049
1980	22.86456
1981	23.01501
1982	15.75569
1983	11.07084
1984	10.62466
1985	14.82245
1986	11.91684
1987	31.96422
1988	28.72468
1989	23.91764
1990	34.68989
1991	31.24938
1992	31.59094
1993	24.28255
1994	29.51155
1995	18.58844
1996	17.44523
1997	13.19969
1998	14.06156
1999	13.82789
2000	18.13484
2001	7.83994
2002	8.54942
2003	13.92135
2004	16.47069
2005	17.57306
2006	16.86538
2007	15.60358
2008	13.51919
2009	13.49977
2010	16.79497
2011	16.26669
2012	32.90533
2013	28.62676
2014	30.76004
2015	19.36254
2016	24.91409