Year	% of total
1970	14.756751424528494
1971	15.182273033689903
1972	15.622500918173458
1973	14.479866687907267
1974	19.373286396551375
1975	17.750601005585544
1976	17.114166781989926
1977	14.488378016821319
1978	17.512447753309278
1979	16.153560641787724
1980	13.353455545439822
1981	16.616193148542685
1982	14.450365996269198
1983	15.956320528880358
1984	16.257526750714334
1985	18.13836839533867
1986	17.768318610260263
1987	17.031281868567547
1988	18.343124554227483
1989	16.67235437355484
1990	14.393939393939394
1991	35.30054644808743
1992	41.06145251396648
1993	44.082687338501295
1994	45.52481692432872
1995	43.83223684210527
1996	42.6464391066161
1997	40.81023454157783
1998	39.03072263089572
1999	37.27472527472527
2000	35.24444444444445
2001	34.47146866230121
2002	33.497536945812804
2003	33.085896076352064
2004	33.80952380952381
2005	31.604938271604937
2006	31.01567825494206
2007	29.97746055597295
2008	29.266211604095567