Year	% of total
1970	41.143170508985556
1971	41.474362104445426
1972	42.44486580236767
1973	43.61734274315261
1974	43.6751416219882
1975	44.037978143561695
1976	43.71585376794852
1977	43.73004764171428
1978	43.095672502357814
1979	43.08369898634994
1980	37.12237156779376
1981	31.681651098304243
1982	31.002264698683497
1983	30.57766360249875
1984	30.79121870185071
1985	28.51309349290284
1986	31.754874632626994
1987	30.31618328993442
1988	30.03277007518935
1989	29.463348096083962
1990	38.46153846153847
1991	38.125
1992	36.96969696969697
1993	35.32934131736527
1994	32.72727272727273
1995	32.35294117647059
1996	32.33532934131736
1997	33.532934131736525
1998	31.446540880503143
1999	33.557046979865774
2000	36.42857142857142
2001	38.68613138686132
2002	38.63636363636363
2003	40.76923076923077
2004	43.41085271317829
2005	46.09375
2006	47.76119402985074
2007	49.275362318840585
2008	51.388888888888886