| Year | Value | | 2023 | 6.2506432215476 | | 2022 | 7.123507733014 | | 2021 | 2.1945743234001 | | 2020 | 0.29055455565324 | | 2019 | 1.0240939296343 | | 2018 | 1.083820984093 | | 2017 | 0.75401504708435 | | 2016 | 0.3566845008917 | | 2015 | 0.20792883990527 | | 2014 | 1.0411962117844 | | 2013 | 1.4782861568881 | | 2012 | 2.8083362256157 | | 2011 | 3.4168075425521 | | 2010 | 1.1841352315465 | | 2009 | -9.1736038443034E-7 | | 2008 | 4.0659535535838 | | 2007 | 2.5106656524034 | | 2006 | 1.5666638070439 | | 2005 | 0.62387445002519 | | 2004 | 0.18712055908442 | | 2003 | 0.87744038625479 | | 2002 | 1.5712201278938 | | 2001 | 2.578440800989 | | 2000 | 3.0421008066779 | | 1999 | 1.1622315566944 | | 1998 | 1.3994737857984 | | 1997 | 1.1925588342584 | | 1996 | 0.62919423812097 | | 1995 | 0.7912394069385 | | 1994 | 1.088556775894 | | 1993 | 2.1906531955644 | | 1992 | 2.9193231928501 | | 1991 | 4.3102128984347 | | 1990 | 6.1495653117985 | | 1989 | 6.5929098018913 | | 1988 | 5.0859286139488 | | 1987 | 4.1130288620506 | | 1986 | 2.9335792044233 | | 1985 | 5.1956219542944 | | 1984 | 7.0676563832817 | | 1983 | 8.3662926064564 | | 1982 | 9.5849276467744 | | 1981 | 11.305756650955 | | 1980 | 11.594619249211 | | 1979 | 7.4669615131074 | | 1978 | 7.7993507455215 | | 1977 | 11.793346918405 | | 1976 | 14.342693085226 | | 1975 | 17.811397234021 | | 1974 | 16.936399998927 |
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