| Year | Value | | 2014 | 13.797970897966 | | 2013 | 12.320705333451 | | 2012 | 16.297868608017 | | 2011 | 33.260288618119 | | 2010 | 23.713984940034 | | 2009 | 41.667245837086 | | 2008 | 45.219326532044 | | 2007 | 47.998391442952 | | 2006 | 42.377003843408 | | 2005 | 47.766170947278 | | 2004 | 46.003816180532 | | 2003 | 49.014634681144 | | 2002 | 53.044100917017 | | 2001 | 51.688784205588 | | 2000 | 45.002409149414 | | 1999 | 40.249672431244 | | 1998 | 18.412902935822 | | 1997 | 8.6998570382049 | | 1996 | 6.2913025091627 | | 1995 | 6.6359163452852 | | 1994 | 9.3307322780736 | | 1993 | 0.097755970740829 | | 1992 | -3.3762506506807 | | 1991 | -2.7836238308042 | | 1990 | 7.9650583526857 | | 1989 | 0.65685207264182 | | 1988 | 0.42061067785824 | | 1987 | -2.5195637751279 | | 1986 | -3.3111957715541 | | 1985 | -3.8158615248284 | | 1984 | -2.2640950568272 | | 1983 | 0.85184194251886 | | 1982 | 1.129029561418 | | 1981 | 0.076429152845332 | | 1980 | -12.258245573825 | | 1979 | -50.543974815334 | | 1978 | -34.853322878562 | | 1977 | -37.406964749864 | | 1976 | -41.390465442433 | | 1975 | -47.195174688738 | | 1974 | -49.218272921798 | | 1973 | -72.518525326366 | | 1972 | -53.634234688018 | | 1971 | -41.699411695535 |
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