Year	% of total
1970	23.174747498837363
1971	22.930635940459123
1972	26.08821007619006
1973	25.50538271242584
1974	21.284506639330584
1975	22.3685355707482
1976	20.481183350026512
1977	21.06218834995467
1978	20.038474514173444
1979	19.73855358309559
1980	17.82484111565156
1981	22.002362210138703
1982	22.019351109497023
1983	22.770322659374592
1984	28.74842295076259
1985	27.849970907072
1986	27.34740687908019
1987	27.21426960347053
1988	25.97011152399698
1989	27.568615450400436