| Year | Value | | 2015 | 6.6118159324936 | | 2014 | -8.0871288854344 | | 2013 | -21.886126236358 | | 2012 | -24.108603324161 | | 2011 | -28.219705963745 | | 2010 | -27.653348531126 | | 2009 | -32.101398110643 | | 2008 | -30.693094992456 | | 2007 | -34.935194699676 | | 2006 | -41.126870599924 | | 2005 | -43.046540722981 | | 2004 | -43.739146391556 | | 2003 | -40.634591748246 | | 2002 | -40.923324067196 | | 2001 | -41.86468790251 | | 2000 | -41.823276238405 | | 1999 | -39.236103034271 | | 1998 | -42.340442379328 | | 1997 | -44.481699840562 | | 1996 | -43.324863455359 | | 1995 | -39.310078943478 | | 1994 | -34.881810779929 | | 1993 | -37.470879910485 | | 1992 | -34.789382106952 | | 1991 | -36.81356788568 | | 1990 | -34.738208594525 | | 1989 | -30.556562405026 | | 1988 | -31.65283740087 | | 1987 | -30.768960337586 | | 1986 | -32.266611183348 | | 1985 | -34.054017740758 | | 1984 | -36.388421326354 | | 1983 | -34.637471573917 | | 1982 | -33.671219948632 | | 1981 | -30.85343375352 | | 1980 | -25.646384033239 | | 1979 | -24.284868900838 | | 1978 | -19.703100818985 | | 1977 | -20.5607777051 | | 1976 | -21.693001073948 | | 1975 | -25.743043269098 | | 1974 | -38.607887200731 | | 1973 | -50.802376230379 | | 1972 | -53.069725646364 | | 1971 | -64.263977902062 |
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