Year	% of total
1970	27.585725709990207
1971	26.223227479663365
1972	23.08580331266472
1973	25.352983729526002
1974	23.2579093468323
1975	21.488645785771826
1976	21.08823715338982
1977	21.548553834729773
1978	22.015576892191994
1979	21.977877796131125
1980	20.304150059698625
1981	19.81780194669915
1982	19.59141383671128
1983	21.208003172174163
1984	20.672032432371957
1985	21.58164351084422
1986	21.90779361677455
1987	15.735764274427
1988	21.47777112083705
1989	22.30583101917003
1990	3.635116598079561
1991	3.6635006784260513
1992	3.4832172260924636
1993	3.4566403881140086
1994	3.3937975424224693
1995	3.3966609096142775
1996	3.372681281618887
1997	3.259098316132537
1998	3.454133635334088
1999	3.3888888888888893
2000	3.686087990487515
2001	3.4636871508379885
2002	3.335126412049489
2003	3.2873806998939554
2004	3.139240506329114
2005	3.194726166328601
2006	3.081510934393638
2007	3.1
2008	3.1219028741328048