| Year | Value | | 2014 | 36.195871416114 | | 2013 | 29.92229960964 | | 2012 | 26.162453408688 | | 2011 | 22.19539285838 | | 2010 | 18.970706391755 | | 2009 | 16.021039038384 | | 2008 | 19.889501531678 | | 2007 | 12.582747460752 | | 2006 | 24.223715896009 | | 2005 | 19.640865122964 | | 2004 | 19.590397097486 | | 2003 | 19.625790321747 | | 2002 | 14.181959799008 | | 2001 | 13.945732439076 | | 2000 | 9.1965545702041 | | 1999 | 4.5129403467582 | | 1998 | 0.58000826928547 | | 1997 | -1.5427351984418 | | 1996 | 2.6224177622389 | | 1995 | 8.1762162443406 | | 1994 | 4.5895842326753 | | 1993 | -8.0903495251715 | | 1992 | -21.214363949045 | | 1991 | -29.853239582264 | | 1990 | -15.784025331256 | | 1989 | -40.076779684185 | | 1988 | -38.423725722185 | | 1987 | -46.830778114541 | | 1986 | -55.261783255442 | | 1985 | -57.397703475828 | | 1984 | -65.987229426125 | | 1983 | -76.934289188663 | | 1982 | -88.39274196368 | | 1981 | -92.097976678208 | | 1980 | -104.17942317773 | | 1979 | -117.30463532249 | | 1978 | -111.86736556795 | | 1977 | -103.75784465419 | | 1976 | -93.729012778347 | | 1975 | -148.54196939732 | | 1974 | -133.1564297396 | | 1973 | -140.75173777724 | | 1972 | -151.00772631629 | | 1971 | -181.01494268147 |
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