Year	% of total
1970	3.653338996644331
1971	3.6891176793960416
1972	4.100779980780382
1973	4.299091960736082
1974	5.091197196688576
1975	4.642466670602184
1976	4.549539859005562
1977	4.300554617448996
1978	4.557403334978898
1979	3.0247331767623296
1980	2.7716177218228113
1981	2.9335987077795824
1982	2.762114616891096
1983	3.2142654723523547
1984	3.6605085058048354
1985	4.114000358830312
1986	3.933302084807017
1987	3.939566574345995
1988	5.276498280109869
1989	5.10901152626756
1990	3.391684901531729
1991	3.4028540065861685
1992	3.5049288061336252
1993	3.567567567567568
1994	3.6055143160127257
1995	3.5160289555325748
1996	5.029013539651837
1997	6.478873239436619
1998	7.550482879719052
1999	8.469055374592834
2000	9.423676012461058
2001	9.780907668231611
2002	9.885057471264368
2003	9.838472834067549
2004	9.336941813261165
2005	9.244791666666668
2006	9.287115761935906
2007	8.930817610062892
2008	8.523409363745499