Year	Percent
1960	27.86155
1961	28.12304
1962	31.8073
1963	29.63823
1964	31.62624
1965	31.3931
1966	31.68724
1967	32.51822
1968	34.47225
1969	34.87766
1970	35.34354
1971	33.78834
1972	32.75488
1973	29.74566
1974	30.1456
1975	31.73895
1976	32.11865
1977	32.36419
1978	30.84326
1979	30.20134
1980	31.69761
1981	25.79837
1982	25.03458
1983	18.59673
1984	20.56524
1985	20.66667
1986	22.94931
1987	26.01439
1988	25.76124
1989	25.86641
1990	21.94063
1991	28.59154
1992	25.43844
1993	30.74465
1994	30.94796
1995	27.33967
1996	28.0748
1997	28.38073
1998	25.78934
1999	25.47447
2000	24.13854
2001	24.88346
2002	24.43665
2003	23.30094
2004	22.58751
2005	16.66919
2006	27.03582
2007	28.63715
2008	30.85427
2009	30.10202
2010	31.0663
2011	31.80853
2012	32.34032
2013	31.33571
2014	29.74206
2015	29.93171
2016	36.3629
2017	35.40364