| Year | Value | | 2014 | -10.781255269246 | | 2013 | -9.8153680578771 | | 2012 | -9.9657394041395 | | 2011 | -18.388824771431 | | 2010 | -18.520618264098 | | 2009 | -18.615419349471 | | 2008 | -19.811200809738 | | 2007 | -20.682610975528 | | 2006 | -19.605919254932 | | 2005 | -18.07273404504 | | 2004 | -16.331472282252 | | 2003 | -13.840447170019 | | 2002 | -13.846591187139 | | 2001 | -14.234664550223 | | 2000 | -14.098732210956 | | 1999 | -8.5087229364838 | | 1998 | -7.8281931360855 | | 1997 | -6.9267110336072 | | 1996 | -6.4896813078334 | | 1995 | -5.8133990775779 | | 1994 | -7.6068432048118 | | 1993 | -8.7931348804923 | | 1992 | -8.4096306372683 | | 1991 | -8.443763580838 | | 1990 | -8.4695237574815 | | 1989 | -9.5076966879806 | | 1988 | -10.081895539595 | | 1987 | -10.916374184988 | | 1986 | -11.595732420999 | | 1985 | -12.35574770139 | | 1984 | -12.397491386671 | | 1983 | -8.2805052663274 | | 1982 | -6.4737591554476 | | 1981 | -4.2749982735109 | | 1980 | 0.49635517621714 | | 1979 | 1.8257270587321 | | 1978 | 4.7167438360127 | | 1977 | 5.447571684541 | | 1976 | 3.8535860697246 | | 1975 | 5.7240022604778 | | 1974 | 4.9392244415235 | | 1973 | 5.4970260726577 | | 1972 | 8.568364620127 | | 1971 | 11.487056136643 |
|