| Year | Value | | 1998 | 1.4924429267059 | | 1997 | 1.1730587506924 | | 1996 | 0.96509741120574 | | 1995 | 1.146181244531 | | 1994 | 1.4227642854782 | | 1993 | 1.0926240655955 | | 1992 | 0.085814810163652 | | 1991 | 0.25560739522038 | | 1990 | 1.545070847151 | | 1989 | 1.1759929111147 | | 1988 | 1.2298205714304 | | 1987 | 1.2673803162233 | | 1986 | 2.0950217689099 | | 1985 | 1.9380025240545 | | 1984 | 3.1286141038017 | | 1983 | 3.2382993300123 | | 1982 | 3.4447790172651 | | 1981 | 3.7361503697171 | | 1980 | 2.6999095026506 | | 1979 | 2.1784263334725 | | 1978 | 7.5979644959313 | | 1977 | 4.6158022211191 | | 1974 | 32.677682472533 | | 1973 | 37.217131101552 | | 1972 | 37.431693989071 |
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