| Year | Value | | 2013 | 0.0023708480523483 | | 2005 | 0.0027862914460853 | | 2004 | 0.0028877530393601 | | 2003 | 0.0029874824485406 | | 2001 | 0.0063173189298462 | | 2000 | 0.024188184072081 | | 1999 | 0.021117094287826 | | 1998 | 0.0036551043532293 | | 1997 | 0.0039904229848364 | | 1996 | 0.049179594938973 | | 1995 | 0.22056661111656 | | 1994 | 1.1733380384483 | | 1993 | 1.0661018135985 | | 1992 | 0.96621438479568 | | 1991 | 1.0215960656672 | | 1990 | 1.0972285324852 | | 1989 | 1.1868917576961 | | 1988 | 1.3339979156283 | | 1987 | 1.1089438734138 | | 1986 | 0.97911957567755 | | 1985 | 0.98639706786707 | | 1984 | 1.4582987437047 | | 1983 | 1.5688809700257 | | 1982 | 1.8208574164037 | | 1981 | 1.8514160194556 | | 1980 | 2.421927761347 | | 1979 | 1.8721386527142 | | 1978 | 1.9063555143873 | | 1977 | 2.2572949164984 | | 1976 | 2.2071642380185 | | 1975 | 3.2424557752341 | | 1974 | 3.3568110295219 | | 1973 | 3.4263726867404 | | 1972 | 3.5848489403277 |
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