| Year | Value | | 1991 | 0.1000000015 | | 1990 | 0.1000000015 | | 1989 | 0.1000000015 | | 1988 | 0.3000000119 | | 1987 | 0.3000000119 | | 1986 | 0.3000000119 | | 1985 | 0.400000006 | | 1984 | 0.400000006 | | 1983 | 0.3000000119 | | 1982 | 0.3000000119 | | 1981 | 0.200000003 | | 1980 | 0.200000003 | | 1979 | 0.1000000015 | | 1978 | 0.1000000015 |
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