| Year | Value | | 1994 | 1.8401863093193 | | 1993 | 1.9450845604031 | | 1992 | 1.6875704622322 | | 1991 | 0.91059602649007 | | 1990 | 0.9520398722655 | | 1989 | 0.95951322256026 | | 1988 | 1.0005093502147 | | 1987 | 0.85900355587518 | | 1986 | 0.88176547961222 | | 1985 | 0.96328424450272 | | 1984 | 1.0325406758448 | | 1983 | 1.2246403541129 | | 1982 | 1.1560693641619 | | 1981 | 2.2416621104429 | | 1980 | 2.1841192080016 | | 1979 | 1.9912251096861 | | 1978 | 2.0018514232816 | | 1977 | 2.4364281490243 | | 1976 | 2.4542318917485 | | 1975 | 3.1911142454161 | | 1974 | 2.0387767339596 | | 1973 | 2.1477098400175 | | 1972 | 2.1636240703178 |
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