Year	% of total
1960	33.46017939657516
1961	30.706865974157594
1962	28.546371409778555
1963	26.5370800760617
1964	25.15170537769408
1965	24.561403508771924
1966	23.082926829268292
1967	23.66717440974867
1968	22.097442985487213
1969	20.988457161437164
1970	19.32798096937259
1971	19.02828528894302
1972	15.465660770031217
1973	16.907571940061
1974	17.307148912122067
1975	15.519439133205863
1976	15.13768446675795
1977	16.677245318946365
1978	17.082134867369767
1979	17.09439528023599
1980	20.27576197387518
1981	20.101553166069298
1982	15.99075062255425
1983	19.408762977300718
1984	23.554674595308885
1985	23.53342428376535
1986	23.833855282676776
1987	23.095584667637066
1988	26.71932452676018
1989	30.548007246376812
1990	35.23503452811575
1991	29.214428281461437
1992	23.69750714512544
1993	23.636823529411764
1994	26.481585641605427
1995	26.977615686274508
1996	32.741665910122556
1997	36.82956091772152
1998	34.59433962264151
1999	34.46720848056537
2000	28.610254917703738
2001	19.365314393148108
2002	19.280180735263915
2003	18.53704868763775
2004	18.800661428832452
2005	18.413973438621678
2006	21.995572304995616
2007	20.10789311090516
2008	24.53800586080586
2009	20.564818724185404
2010	23.720840504876648
2011	27.285510657774292
2012	29.93307300293031
2013	30.64381118881119
2014	31.941638957978796
2015	33.16270708795901
2016	31.358467966573816