Year	% of total
1970	28.08483937127093
1971	27.88820553471782
1972	29.057144615807022
1973	28.770621243015924
1974	29.718333565919657
1975	31.16426260729733
1976	29.54555612915363
1977	30.03052372896906
1978	30.27895141694541
1979	25.662645069427835
1980	24.645061747228386
1981	24.944271306623364
1982	28.37545498104406
1983	27.637071494327614
1984	26.62964282765189
1985	25.279702309447536
1986	24.763920973078037
1987	24.14681799243891
1988	23.341991752111632
1989	20.23890289714949
1990	27.478981918691698
1991	26.944003627295398
1992	26.547425474254744
1993	25.635079582586695
1994	25.061576354679804
1995	25.355450236966824
1996	25.251470867337254
1997	24.741017265515634
1998	25.121259266038255
1999	24.573916265283437
2000	24.544008979515482
2001	25.560197493353588
2002	26.714175654853623
2003	26.699931513550535
2004	27.931769722814497
2005	28.684003152088263
2006	28.420741324921135
2007	27.783360128617364
2008	27.68033212247016