Year	Percent
1960	32.62721
1961	31.66281
1962	30.7684
1963	45.39366
1964	35.95148
1965	37.2973
1966	39.56953
1967	48.05391
1968	49.24551
1969	54.05086
1970	37.98882
1971	52.33111
1972	72.25788
1973	57.66603
1974	43.26069
1975	47.90225
1976	46.09929
1977	51.2605
1978	46.92136
1979	37.40304
1980	31.63017
1981	40.69557
1982	39.66692
1983	43.54252
1984	40.20049
1985	57.28091
1986	54.70434
1987	45.21951
1988	41.79144
1989	41.19805
1990	30.85894
1991	33.27148
1992	33.79329
1993	34.54842
1994	38.25105
1995	35.7477
1996	33.00766
1997	37.23225
1998	48.56843
1999	38.11895
2000	32.66975
2001	29.36338
2002	32.15018
2003	28.37317
2004	26.72838
2005	23.94093
2006	28.07759
2007	26.60387
2008	26.79916
2009	31.33232
2010	31.49406
2011	28.75338
2012	31.39223
2013	33.27772
2014	28.99992
2015	27.91792
2016	27.03535
2017	26.74608