Year	Percent
1960	33.70487
1961	33.73772
1962	34.8155
1963	32.76855
1964	31.47039
1965	32.13042
1966	32.8593
1967	32.82675
1968	32.61808
1969	31.42446
1970	30.85473
1971	29.46755
1972	30.48826
1973	28.33169
1974	25.7302
1975	19.2362
1976	18.84934
1977	18.8141
1978	20.40384
1979	30.10951
1980	23.39769
1981	34.77155
1982	32.56028
1983	30.39726
1984	31.15304
1985	34.28478
1986	31.10826
1987	32.00042
1988	31.68083
1989	31.13084
1990	30.48031
1991	32.54275
1992	33.63237
1993	33.13131
1994	33.48835
1995	33.30673
1996	35.16017
1997	36.73972
1998	36.22998
1999	37.82271
2000	44.67028
2001	44.77966
2002	47.74139
2003	46.53787
2004	52.03235
2005	45.31225
2006	47.11979
2007	46.9261
2008	46.89588
2009	46.22875
2010	48.48445
2011	47.56058
2012	45.79338
2013	46.7224
2014	47.13017
2015	47.93046
2016	47.5726
2017	47.11705