| Year | Value | | 2022 | 11.513119838051 | | 2021 | 7.3703475887662 | | 2020 | 5.9312763656244 | | 2019 | 7.1156762563119 | | 2018 | 6.5209682394657 | | 2017 | 8.0341897454591 | | 2016 | 7.2287927205792 | | 2015 | 6.8084549457961 | | 2014 | 5.9479993569663 | | 2013 | 5.6991298963738 | | 2012 | 4.254321998139 | | 2011 | 4.7958826618311 | | 2010 | 5.049680758574 | | 2009 | 4.5615068767098 | | 2008 | 4.4436549094501 | | 2007 | 5.3691347380196 | | 2006 | 2.0565034236599 | | 2005 | 4.8386217754316 | | 2004 | 14.206743284557 | | 2003 | 17.032866543199 | | 2002 | 8.6091247438633 | | 2001 | 4.4925960923975 | | 2000 | 0.8449695667737 | | 1999 | 3.8123720536602 | | 1998 | 1.1141884117471 | | 1997 | 2.7812279002323 | | 1996 | 1.0994887077102 | | 1995 | 6.9809744183056 | | 1994 | 1.7102063230564 | | 1993 | 6.4638042275385 | | 1992 | 9.4865425061716 | | 1991 | 8.6423432597344 | | 1990 | 12.16778411307 | | 1989 | 8.2750160875159 | | 1988 | 11.690586887676 | | 1987 | 23.529166955694 | | 1986 | 56.560172013504 | | 1985 | 18.319884874273 | | 1984 | 22.098459414533 | | 1983 | 10.636303676138 | | 1982 | 10.855845455309 | | 1981 | 5.9442270061444 | | 1980 | 6.824615652478 | | 1979 | 6.1289577073428 | | 1978 | 8.8553459121409 | | 1977 | 12.389730830129 | | 1976 | 17.027331083252 | | 1975 | 25.9249999995 | | 1974 | 9.2363103596685 | | 1973 | 6.9186084458902 | | 1972 | 8.6981199007943 | | 1971 | 3.0562257804501 | | 1970 | -1.9850938796199 | | 1969 | 5.0120409388402 | | 1968 | 4.1787534301289 | | 1967 | 1.4072189538168 | | 1966 | 0.23908192532822 | | 1965 | 1.2180366216886 | | 1964 | -4.5356537812368 | | 1963 | 4.6161282529872 | | 1962 | 1.7876178761052 |
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