Year	% of total
1970	21.582092784517513
1971	22.314360490052852
1972	22.09167693999735
1973	21.187654317558795
1974	20.138424673916433
1975	18.988975965790768
1976	17.4597047782901
1977	16.345004137274675
1978	15.58362099058877
1979	15.04728195139709
1980	14.375562969312439
1981	13.553537018577511
1982	12.897455595346708
1983	12.294004700772131
1984	11.936123567413798
1985	11.220191312391208
1986	10.68790818388942
1987	10.440268872084795
1988	9.771479851389056
1989	9.596917438492962
1990	11.138537488429497
1991	11.752988047808765
1992	8.589647411852964
1993	11.039743075070254
1994	12.773403324584425
1995	12.5879917184265
1996	12.327688066167783
1997	10.16494054468738
1998	10.353627415238789
1999	11.210762331838566
2000	12.320730117340286
2001	12.18836565096953
2002	13.054755043227665
2003	14.007571660356948
2004	14.080164439876668
2005	15.062317687616018
2006	16.174055829228244
2007	15.909090909090908
2008	18.00235710076606