Year	% of total
1970	29.26287806988664
1971	29.411203453717714
1972	28.806973338169783
1973	28.98349223175178
1974	29.4033741483217
1975	29.47430237172516
1976	31.12863776187006
1977	32.43868537689789
1978	34.089789122459194
1979	35.44736360118888
1980	37.8758183511239
1981	40.22725972115042
1982	41.05044231618301
1983	41.686158810579144
1984	44.579212210046116
1985	46.51424666669863
1986	46.69980985199237
1987	46.15516396795273
1988	46.84996313761758
1989	45.714831742262255
1990	21.33063609799955
1991	21.4554302145543
1992	21.765868658027674
1993	22.24664761486041
1994	22.63157894736842
1995	21.682626538987687
1996	20.211019929660022
1997	18.83211678832117
1998	17.25006295643415
1999	15.800636267232237
2000	14.177852348993289
2001	15.09988249118684
2002	13.967230727907602
2003	14.55223880597015
2004	14.713610089332633
2005	14.350453172205437
2006	14.091252835896142
2007	13.447432762836186
2008	13.026819923371647