| Year | Value | | 2014 | 46.590707127627 | | 2013 | 45.125907095508 | | 2012 | 44.156488070624 | | 2011 | 43.711480545636 | | 2010 | 43.755173319903 | | 2009 | 41.967455195423 | | 2008 | 40.812877553343 | | 2007 | 41.222259232784 | | 2006 | 38.043059553101 | | 2005 | 33.097185795137 | | 2004 | 34.818319979281 | | 2003 | 33.926861699898 | | 2002 | 31.673683009839 | | 2001 | 29.325136847856 | | 2000 | 27.108444673092 | | 1999 | 22.232050079392 | | 1998 | 15.970461499322 | | 1997 | 15.408435391953 | | 1996 | 10.60486231319 | | 1995 | 0.25803587380823 | | 1994 | -2.3892714888089 | | 1993 | -3.8857108615045 | | 1992 | -3.0066713340932 | | 1991 | -6.9275126195702 | | 1990 | -6.7570569097372 | | 1989 | -5.4995031087164 | | 1988 | -6.641217792233 | | 1987 | -11.741569938115 | | 1986 | -14.341231119736 | | 1985 | -10.443362909875 | | 1984 | 8.7359048428207 | | 1983 | 7.6065323994702 | | 1982 | -7.6539772076509 | | 1981 | -8.0545193453472 | | 1980 | 10.422830948948 | | 1979 | 10.383983764297 | | 1978 | 10.907232720157 | | 1977 | 9.43184949282 | | 1976 | 8.1376148538984 | | 1975 | 12.695668396649 | | 1974 | 11.950985934612 | | 1973 | 11.81404514814 | | 1972 | 11.697405050276 | | 1971 | 9.2973796763374 |
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