Year	Percent
1960	13.39286
1961	14.65517
1962	16.39344
1963	14.28571
1964	12.08054
1965	12.53429
1966	12.99218
1967	11.88578
1968	13.36681
1969	12.09457
1970	11.62102
1971	14.17168
1972	15.07497
1973	13.33273
1974	15.53394
1975	19.00177
1976	16.65288
1977	17.29142
1978	20.2264
1979	22.72214
1980	23.29207
1981	22.0377
1982	26.90745
1983	24.74776
1984	23.55231
1985	20.7869
1986	22.31563
1987	25.73863
1988	25.95318
1989	22.94357
1990	27.77515
1991	28.50518
1992	29.47695
1993	27.16104
1994	28.48176
1995	27.27828
1996	15.7534
1997	14.43991
1998	19.44028
1999	15.96399
2000	16.23475
2001	15.78484
2002	16.98803
2003	20.9949
2004	24.62337
2005	33.44431
2006	46.86974
2007	34.22384
2008	37.92616
2009	43.12351
2010	39.17905
2011	37.66549
2012	37.46885
2013	34.24535
2014	33.53882
2015	29.74058
2016	31.91536