Year	% of total
1971	16.89189189189189
1972	14.02439024390244
1973	12.834224598930483
1974	11.538461538461538
1975	7.5892857142857135
1976	9.25925925925926
1977	7.792207792207792
1978	7.936507936507936
1979	7.323943661971831
1980	7.605633802816901
1981	8.56353591160221
1982	11.84573002754821
1983	8.62533692722372
1984	7.631578947368421
1985	14.795918367346939
1986	16.62870159453303
1987	15.195071868583163
1988	13.090909090909092
1989	9.507640067911714
1990	20.256410256410255
1991	21.236872812135356
1992	20.537634408602152
1993	17.18907987866532
1994	15.553435114503817
1995	15.265866209262436
1996	17.674783974862528
1997	17.8699070764832
1998	20.806241872561767
1999	18.86435331230284
2000	24.24071991001125
2001	25.013082155939298
2002	23.17948717948718
2003	21.565802113352543
2004	21.709006928406467
2005	19.93838028169014
2006	18.97872340425532
2007	18.98580121703854
2008	19.006648416112633
2009	18.897943344974777
2010	20.565265898103384
2011	18.161845477846942
2012	18.055058991776903
2013	17.31301939058172
2014	17.194416070820566
2015	18.651985318651985