| Year | Value | | 1999 | 0.97413650131369 | | 1998 | 0.95129201920878 | | 1997 | 1.1701705672352 | | 1996 | 1.0855923021637 | | 1995 | 1.115756889741 | | 1994 | 1.1925565578803 | | 1993 | 1.1986452287121 | | 1992 | 1.0834742674861 | | 1991 | 1.2285473131389 | | 1990 | 1.2563591365324 | | 1989 | 2.0849104859335 | | 1988 | 2.1109857421274 | | 1987 | 1.8409804373659 |
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