| Year | Value | | 1994 | 13.405072784355 | | 1993 | 4.6544917843957 | | 1992 | 6.9048094567737 | | 1991 | 7.3011970620549 | | 1990 | 2.3221744925371 | | 1989 | 9.1489428401469 | | 1988 | 13.331447443903 | | 1987 | 10.761008501945 | | 1986 | 5.3624100279825 | | 1985 | 3.8518115434006 | | 1984 | 7.325172262832 | | 1983 | 13.17002324573 | | 1982 | 8.0931392702396 | | 1978 | 22.999793036194 | | 1977 | 23.262678096308 |
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