Year	% of total
1970	18.415189695455748
1971	20.189046954068235
1972	21.510850613954208
1973	22.505088417061554
1974	23.79526530544655
1975	24.716197427325184
1976	25.548264301128533
1977	25.295256635360904
1978	23.470674173920578
1979	23.594852071722915
1980	22.73632893214842
1981	21.767659182115633
1982	19.64617388668084
1983	19.91341782331198
1984	20.481711051136248
1985	21.293177339518603
1986	22.373634139604505
1987	21.35020605543973
1988	19.28425868349388
1989	22.25257127548128
1990	8.958990536277604
1991	9.082397003745319
1992	9.188846641318124
1993	9.554551323434474
1994	9.851239669421489
1995	10.394870064124198
1996	10.831321145222491
1997	9.008354522339266
1998	8.950733358405415
1999	8.549019607843137
2000	8.524590163934425
2001	8.67003367003367
2002	8.73015873015873
2003	9.049360146252285
2004	8.97196261682243
2005	10.084451068057627
2006	10.588235294117647
2007	12.316269640141916
2008	14.066369489846458