Year	% of total
1970	0.2236689202177029
1971	0.45689311157651225
1972	0.3993038008387141
1973	0.37448044969181354
1974	0.43860763810764414
1975	0.3896846161083929
1976	0.47057238214434705
1977	0.4336219998133297
1978	0.44475121008816615
1979	0.35354604474151297
1980	0.42506302861927725
1981	0.485444087505373
1982	0.4353985754909683
1983	0.4551639559862682
1984	0.6308664669234793
1985	0.6977234420537286
1986	0.7683917998351135
1987	0.5330029477500916
1988	0.9118964580842462
1989	0.8240426231187523
1990	5.010438413361169
1991	5.627705627705628
1992	6
1993	6.378132118451026
1994	6.359649122807018
1995	6.352459016393443
1996	5.944055944055944
1997	6.7889908256880735
1998	8.064516129032258
1999	8.829568788501026
2000	9.766454352441615
2001	7.9447322970639025
2002	7.6923076923076925
2003	19.742489270386265
2004	17.692307692307693
2005	14.603174603174605
2006	11.401425178147269
2007	15.937499999999998
2008	6.8741893644617384