| Year | Value | | 2022 | 8.6409110897385 | | 2021 | 4.2663575447981 | | 2020 | 2.4194218945778 | | 2019 | 2.5575447570333 | | 2018 | 3.2160538314457 | | 2017 | 3.326033925187 | | 2016 | 2.3510219748583 | | 2015 | 3.3940153841056 | | 2014 | 3.5892201661666 | | 2013 | 3.9847123554813 | | 2012 | 4.2794999964197 | | 2011 | 5.5538989225749 | | 2010 | 4.1232285607532 | | 2009 | 3.7301478656316 | | 2008 | 9.8658853934981 | | 2007 | 5.843975705316 | | 2006 | 5.3949357654489 | | 2005 | 4.8217005071285 | | 2004 | 4.7697907186684 | | 2003 | 4.388365160794 | | 2002 | 4.2971520392957 | | 2001 | 5.4724943594422 | | 2000 | 4.7830567981733 | | 1999 | 5.197551691745 | | 1998 | 7.6732289567508 | | 1997 | 7.1451116088393 | | 1996 | 9.7996833901608 | | 1995 | 14.5838224334 | | 1994 | 22.705647224337 | | 1993 | 14.330803336589 | | 1992 | 13.637424171722 | | 1991 | 19.505001673093 | | 1990 | 16.192137561523 | | 1989 | 12.670042091136 | | 1988 | 10.832703768991 | | 1987 | 10.751858992074 | | 1986 | 12.37160916513 | | 1985 | 11.52126073685 | | 1984 | 12.447569329185 | | 1983 | 11.690925802972 | | 1982 | 10.66761431957 | | 1981 | 13.580257784764 | | 1980 | 17.603479542129 | | 1979 | 13.293658653321 | | 1978 | 10.306129222296 | | 1977 | 11.904780430627 | | 1976 | 10.246023002153 | | 1975 | 13.019213106846 | | 1974 | 19.42771084352 | | 1973 | 12.796894532602 | | 1972 | 5.4277029963075 | | 1971 | 3.6746143057503 |
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