Year	% of total
1970	35.579477354807146
1971	32.33718504472242
1972	31.366303753934005
1973	28.644990873018365
1974	28.390581313512335
1975	23.409172840853135
1976	14.82232452962502
1977	16.422217841538817
1978	17.688548705112908
1979	23.380030904706807
1980	20.745257961065143
1981	21.769074598750198
1982	21.876059272670023
1983	22.65107020327404
1984	14.544347696610602
1985	15.633430854864795
1986	14.511588821466153
1987	15.243104614794586
1988	15.632249083343632
1989	18.135457864250277
1990	14.743589743589745
1991	16.16766467065868
1992	17.415730337078653
1993	17.647058823529413
1994	18.68686868686869
1995	17.391304347826086
1996	16.030534351145036
1997	14.726027397260275
1998	13.93188854489164
1999	13.239436619718308
2000	12.467532467532468
2001	12.46819338422392
2002	13.75921375921376
2003	14.182692307692307
2004	13.947990543735225
2005	14.318706697459586
2006	13.656387665198238
2007	13.445378151260504
2008	13.572854291417165