Year	% of total
1970	19.21781579377167
1971	18.52893801066047
1972	18.023029648216202
1973	17.58529926052089
1974	16.826497349682786
1975	17.25205190871792
1976	17.488735986721082
1977	17.95769629465191
1978	18.010763470132662
1979	18.492966962004882
1980	18.96739006128872
1981	20.23015010648404
1982	22.103689166286543
1983	23.00764808369099
1984	23.403394250513347
1985	24.231668639392538
1986	26.09063698909812
1987	27.766942349452446
1988	28.74430158045836
1989	31.259623898730958
1990	53.97148676171079
1991	55.85774058577406
1992	62.64775413711584
1993	59.45945945945946
1994	58.719646799117
1995	58.77192982456141
1996	59.08096280087527
1997	59.08096280087527
1998	57.826086956521735
1999	54.9792531120332
2000	57.173913043478265
2001	57.268722466960355
2002	54.736842105263165
2003	57.391304347826086
2004	55.907172995780584
2005	55.09355509355509
2006	58.61297539149888
2007	61.882352941176464
2008	68.83116883116884