Year	% of total
1970	6.799946386694645
1971	6.8705382251248555
1972	8.300463981091358
1973	9.106934137715244
1974	10.940600352454695
1975	11.461446237993595
1976	11.203468725426168
1977	12.111995872835877
1978	12.634516735301288
1979	11.455846124852156
1980	10.417088910101016
1981	10.07672901173276
1982	10.090164626601702
1983	10.352531732276967
1984	11.304574661498142
1985	13.266896266232669
1986	14.18745387667272
1987	14.696817033074202
1988	16.912302017809004
1989	16.850037952940536
1990	9.75609756097561
1991	10
1992	10.256410256410255
1993	10
1994	10.256410256410255
1995	12.82051282051282
1996	12.5
1997	12.195121951219512
1998	11.904761904761903
1999	13.953488372093023
2000	14.285714285714285
2001	15
2002	14.634146341463413
2003	15
2004	17.5
2005	17.5
2006	16.666666666666664
2007	15.909090909090908
2008	15.909090909090908