| Year | Value | | 2022 | 3.9806496199031 | | 2021 | 3.4236294760919 | | 2020 | 2.101729548274 | | 2019 | 1.0918480265586 | | 2018 | 0.54313314819957 | | 2017 | 2.1718329851001 | | 2016 | 3.1983977665837 | | 2015 | 3.2717016609213 | | 2014 | 2.9089267285863 | | 2013 | 2.6822968408504 | | 2012 | 3.2551460028721 | | 2011 | 4.8394034987095 | | 2010 | 4.4964028776979 | | 2009 | 4.6095954844779 | | 2008 | 10.582709786514 | | 2007 | 5.484949832776 | | 2006 | 3.0570133916672 | | 2005 | 4.1429758363102 | | 2004 | 1.2485644367989 | | 2003 | 0.96135029354211 | | 2002 | 0.88845014807491 | | 2001 | 1.3 | | 2000 | 1.8129461388709 | | 1999 | 2.9908103592317 | | 1998 | 0.12965828767403 | | 1997 | 0.6821914347076 | | 1996 | 3.5539856968429 | | 1995 | 2.6867275658248 | | 1994 | 2.5344352617079 | | 1993 | 0.38254136516592 | | 1992 | 0.54547121378821 | | 1991 | 9.0581883623276 | | 1990 | 9.833635315434 | | 1989 | 3.3420335905579 | | 1988 | 1.4681328804191 | | 1987 | 0.65484469170166 | | 1986 | 0.95360674019204 | | 1985 | 1.4903218142788 | | 1984 | 1.1774600504667 | | 1983 | 4.7181680927516 | | 1982 | 7.7767984269085 | | 1981 | 7.3747815958381 | | 1980 | 6.9282266856319 | | 1979 | 7.0499999992501 | | 1978 | 8.6897451227484 | | 1977 | 9.889519259331 | | 1976 | 5.2350427353238 | | 1975 | 8.3923705721845 | | 1974 | 12.992610837519 | | 1973 | 8.2666666660001 |
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