Year	Percent
1960	13.05685
1961	11.40474
1962	11.35132
1963	12.2978
1964	12.24908
1965	13.27761
1966	14.3402
1967	14.04775
1968	13.6991
1969	16.07998
1970	14.35585
1971	10.83802
1972	9.55977
1973	13.30187
1974	19.53278
1975	24.11282
1976	23.94164
1977	19.72749
1978	19.819
1979	22.12796
1980	21.67128
1981	15.54287
1982	18.61312
1983	23.42297
1984	22.80096
1985	26.25105
1986	27.32017
1987	28.34394
1988	32.47347
1989	33.70002
1990	32.49458
1991	31.30102
1992	28.96179
1993	25.88068
1994	27.46324
1995	28.62625
1996	26.64554
1997	26.47045
1998	25.52113
1999	28.76613
2000	30.5317
2001	32.39863
2002	32.80393
2003	35.65905
2004	39.80237
2005	40.15982
2006	43.79511
2007	45.069
2008	41.42417
2009	37.04077
2010	37.74511
2011	37.76196
2012	34.12186
2013	32.19947
2014	33.10536
2015	29.36667
2016	28.18356
2017	28.70361