| Year | Value | | 2022 | 11.643866711056 | | 2021 | 4.5245683825912 | | 2020 | 3.0454908480433 | | 2019 | 2.5575447570333 | | 2018 | 2.4348898135306 | | 2017 | 2.1827184686852 | | 2016 | 3.7861935589312 | | 2015 | 4.3487735321705 | | 2014 | 4.7186752785466 | | 2013 | 1.7895555398459 | | 2012 | 3.0074484021305 | | 2011 | 3.341216942593 | | 2010 | 1.4107110795432 | | 2009 | 0.35304517836096 | | 2008 | 8.7162687303961 | | 2007 | 4.4077993839804 | | 2006 | 3.3920173369941 | | 2005 | 3.0525762138785 | | 2004 | 1.0547387140351 | | 2003 | 2.8101787574361 | | 2002 | 2.4893981665071 | | 2001 | 3.5691005300146 | | 2000 | 3.8432729570658 | | 1999 | 3.3368791752602 | | 1998 | 5.1102495451756 | | 1997 | 6.1338646435793 | | 1996 | 7.3591178178878 | | 1995 | 8.232630341161 | | 1994 | 11.443119644497 | | 1993 | 12.727766949096 | | 1992 | 15.425806468893 | | 1991 | 21.784412427776 | | 1990 | 26.036481136236 | | 1989 | 17.027936730896 | | 1988 | 14.684351250082 | | 1987 | 19.88084572019 | | 1986 | 19.476837923258 | | 1985 | 30.703498909615 | | 1984 | 19.860205660263 | | 1983 | 27.25719467262 | | 1982 | 9.9410269304184 | | 1981 | 19.686832708432 | | 1980 | 35.138340533048 | | 1979 | 33.389219010225 | | 1978 | 40.087224631385 | | 1977 | 91.954132556511 | | 1976 | 211.9243022259 | | 1975 | 374.73527423263 | | 1974 | 504.73854121598 | | 1973 | 352.81098657303 | | 1972 | 77.79574047552 | | 1971 | 20.052231204054 |
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