Year	Percent
1960	17.38846
1961	15.8631
1962	13.67864
1963	12.45991
1964	16.33037
1965	16.47576
1966	17.61259
1967	19.6589
1968	20.51275
1969	21.05006
1970	21.20147
1971	21.32281
1972	21.50599
1973	20.65781
1974	24.03376
1975	35.37989
1976	28.23008
1977	29.09277
1978	22.22003
1979	16.05949
1980	28.74665
1981	27.94338
1982	20.97325
1983	24.19629
1984	16.6207
1985	14.2888
1986	10.41324
1987	8.72745
1988	14.29882
1989	18.10776
1990	23.80183
1991	30.36985
1992	27.23334
1993	20.63075
1994	13.32294
1995	13.468
1996	15.02617
1997	15.37163
1998	16.54484
1999	15.59339
2000	19.79019
2001	21.23225
2002	23.75878
2003	26.05163
2004	26.04693
2005	24.10968
2006	23.29832
2007	21.04369
2008	21.65228
2009	20.98809
2010	19.37099
2011	17.55834
2012	23.24419
2013	23.44954
2014	21.46356
2015	19.27391
2016	20.81043
2017	22.28541