| Year | Value | | 2009 | 0.0046057027196982 | | 2008 | 0.059256280603777 | | 2007 | 0.010684358935246 | | 2006 | 0.17007254657065 | | 2004 | 1.1113638073463 | | 2003 | 3.7917365932232 | | 2002 | 4.3274839202749 | | 2001 | 5.2831612512511 | | 2000 | 5.5992732234319 | | 1999 | 6.3330423819222 | | 1998 | 6.4355312142577 | | 1997 | 6.1113104872672 | | 1996 | 6.5376205743771 | | 1995 | 6.1531398008828 | | 1994 | 32.261355355842 | | 1993 | 39.224844720497 | | 1992 | 41.841759684833 | | 1991 | 42.623250152161 | | 1990 | 42.829049976266 | | 1989 | 42.644165279249 | | 1988 | 41.55965643337 | | 1987 | 41.128307538692 | | 1986 | 39.064918980287 | | 1985 | 36.80690399137 | | 1984 | 32.869666861484 | | 1983 | 32.071071626874 | | 1982 | 35.325971543852 | | 1981 | 38.068980430317 | | 1980 | 42.06937095826 | | 1978 | 39.692832764505 | | 1977 | 40.255722829449 | | 1976 | 41.608040201005 | | 1975 | 39.570641137221 | | 1974 | 42.723631508678 | | 1973 | 38.275124732716 | | 1972 | 41.652684563758 |
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