| Year | Value | | 1994 | 0.010341842871435 | | 1993 | 0.017260096020639 | | 1992 | 0.020971283804143 | | 1991 | 0.015382810361235 | | 1990 | 0.014319655626894 | | 1989 | 0.018024985907738 | | 1988 | 0.056358708347392 | | 1987 | 0.04143498716852 | | 1986 | 0.046290610563706 | | 1985 | 0.045426412051627 | | 1984 | 0.045278337726779 | | 1983 | 0.049236136510705 | | 1982 | 0.058907007256272 | | 1981 | 0.050531151306345 | | 1980 | 0.090154812717463 | | 1979 | 0.14530941217499 | | 1978 | 0.17955470433325 | | 1977 | 0.25967894239849 | | 1976 | 1.4776828110161 | | 1975 | 0.74070155018253 | | 1974 | 0.30251141552511 | | 1973 | 0.70866754925629 |
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