| Year | Value | | 2022 | 10.77375122429 | | 2021 | 4.0285288815738 | | 2020 | 2.5808007718283 | | 2019 | 0.40565519030955 | | 2018 | 3.2160538314457 | | 2017 | 3.6669970267593 | | 2016 | 0.97767513471897 | | 2015 | 1.2865497076024 | | 2014 | 3.2176919199468 | | 2013 | 3.5432957393484 | | 2012 | 3.8521603331598 | | 2011 | 6.5224925486934 | | 2010 | 2.9323630136986 | | 2009 | 2.5160912814511 | | 2008 | 9.7322831714688 | | 2007 | 8.827292723933 | | 2006 | 8.9135010565015 | | 2005 | 4.9371700498179 | | 2004 | 4.7103706010588 | | 2003 | 3.9210535755819 | | 2002 | 6.4193337222115 | | 2001 | 5.3893442622951 | | 2000 | 4.1992882562281 | | 1999 | 6.9091462486678 | | 1998 | 6.8107932379719 | | 1997 | 6.833343349961 | | 1996 | 6.5509733606557 | | 1995 | 6.0293318848453 | | 1994 | 7.3234715441229 | | 1993 | 10.51783844729 | | 1992 | 4.6435192988371 | | 1991 | 7.0010137754188 | | 1990 | 13.488088792637 | | 1989 | 12.670042091136 | | 1988 | 9.1593141335106 | | 1987 | 0.5187416331999 | | 1986 | 1.6326530612248 | | 1985 | 6.6987039465849 | | 1984 | 7.3891625616947 | | 1983 | 5.5894980184394 | | 1982 | 11.415693128365 | | 1981 | 14.461591074211 | | 1980 | 41.99951438657 | | 1979 | 14.46637020583 | | 1978 | 8.5451391508229 | | 1977 | 9.172498970748 | | 1976 | 12.955729167184 | | 1975 | 14.738323271755 | | 1974 | 29.115630311092 | | 1973 | 13.450797872678 | | 1972 | 5.3959355293341 | | 1971 | 0.31634446369248 | | 1970 | 1.5418659432567 | | 1969 | 2.3152205667647 | | 1968 | 6.9771075867297 | | 1967 | 1.8785321978165 | | 1966 | 2.5048955609584 | | 1965 | 1.7855659829823 | | 1964 | 1.89557417281 |
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