| Year | Value | | 2020 | 37.387432958483 | | 2019 | 57.73107709452 | | 2016 | 32.01971948619 | | 2015 | 40.602444255923 | | 2014 | 53.704315461749 | | 2013 | 57.850176448547 | | 2012 | 57.501725850053 | | 2011 | 50.089826227892 | | 2010 | 54.044306337166 | | 2009 | 40.192057214549 | | 2008 | 43.49245367008 | | 2007 | 33.348470798809 | | 2006 | 42.004904226197 | | 2005 | 32.69808848125 | | 2004 | 17.045043350692 | | 2003 | 30.741573447339 | | 2002 | 23.548273703979 | | 2001 | 22.025235322168 | | 2000 | 36.172629740432 | | 1999 | 17.682095742889 | | 1998 | 6.0243474479335 | | 1997 | 9.2748130116751 | | 1996 | 0.20924828871762 | | 1995 | -2.3017496682331 | | 1994 | 28.80795329889 | | 1993 | 21.211464255284 | | 1992 | 32.332102073079 | | 1991 | 17.578389748812 | | 1990 | 31.77735958007 | | 1989 | 14.599500740259 | | 1988 | 5.3517770563592 | | 1987 | 24.995917994676 | | 1986 | 18.349949213734 | | 1985 | 24.87331120734 | | 1984 | 40.487524611313 | | 1983 | 36.134137725238 | | 1982 | 39.250600449937 | | 1981 | 25.047287983244 | | 1980 | 26.120984350839 | | 1979 | 17.91013446945 | | 1978 | 8.1299100812088 |
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