Year	% of total
1970	19.471830615591394
1971	18.77125285344047
1972	19.3391897730947
1973	19.772984673599147
1974	19.8012796897622
1975	22.047076896113918
1976	22.166266315534838
1977	24.436724843475425
1978	26.66898539302168
1979	27.445731704303405
1980	26.858060300624174
1981	27.272965242761376
1982	28.326976715313755
1983	29.219457933542277
1984	31.046197179010367
1985	32.246726929972915
1986	32.36444002032286
1987	32.59132942019479
1988	33.81213203206103
1989	34.29667468946841
1990	29.657419831859134
1991	29.74416945913575
1992	29.992283745310377
1993	30.342151116743228
1994	30.28242745427519
1995	31.066441229882898
1996	31.779671303376787
1997	34.80858373435388
1998	35.55533710971579
1999	36.712325449018394
2000	38.19867166499922
2001	40.12157685914314
2002	42.01051360548366
2003	43.90312657033251
2004	44.833072194769194
2005	46.05035395800255
2006	48.375520738996556
2007	50.882199748252965
2008	52.434314591507636