| Year | Value | | 2014 | -11.618766587929 | | 2013 | -14.467080430125 | | 2012 | -15.106408565758 | | 2011 | -20.14452555625 | | 2010 | -19.273959017931 | | 2009 | -19.973719713032 | | 2008 | -22.021936367163 | | 2007 | -24.21956100284 | | 2006 | -25.181406285405 | | 2005 | -24.089409021436 | | 2004 | -22.242518358734 | | 2003 | -22.45670664126 | | 2002 | -19.180216678502 | | 2001 | -20.49078498419 | | 2000 | -22.250948728849 | | 1999 | -21.603443724626 | | 1998 | -24.174921890452 | | 1997 | -24.527722503868 | | 1996 | -24.570685820007 | | 1995 | -23.433092650126 | | 1994 | -24.870520300147 | | 1993 | -22.814822405604 | | 1992 | -21.920847658691 | | 1991 | -18.57729813547 | | 1990 | -18.945720682163 | | 1989 | -42.442693156934 | | 1988 | -40.421982763673 | | 1987 | -39.125622848792 | | 1986 | -36.976837603737 | | 1985 | -41.667431921243 | | 1984 | -44.902354704587 | | 1983 | -43.616576938714 | | 1982 | -40.580432573474 | | 1981 | -39.158180077306 | | 1980 | -47.687301692976 | | 1979 | -70.941891629497 | | 1978 | -93.559753212008 | | 1977 | -101.47976190977 | | 1976 | -107.40067842248 | | 1975 | -99.819154659236 | | 1974 | -118.9602524226 | | 1973 | -120.77263251051 | | 1972 | -110.47233221761 | | 1971 | -96.850257680439 |
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