| Year | Value | | 2022 | 49.721102111433 | | 2021 | 7.0147807123816 | | 2020 | 6.1539450839174 | | 2019 | 3.5283935823184 | | 2018 | 2.1350377371319 | | 2017 | 7.704137678506 | | 2016 | 3.9588884659307 | | 2015 | 3.7683678306211 | | 2014 | 3.1790022823606 | | 2013 | 6.9084503482843 | | 2012 | 7.5429137323944 | | 2011 | 6.7167684358855 | | 2010 | 6.2176488930462 | | 2009 | 3.4649632210607 | | 2008 | 22.564495530013 | | 2007 | 15.842111492484 | | 2006 | 10.020183605703 | | 2005 | 11.639686097112 | | 2004 | 7.5759258299586 | | 2003 | 6.3146378705117 | | 2002 | 9.5510316700725 | | 2001 | 14.15845579912 | | 2000 | 6.1762759101204 | | 1999 | 4.6917056304844 | | 1998 | 9.3642430068323 | | 1997 | 9.5736962640516 | | 1996 | 15.935831044721 | | 1995 | 7.674848734498 | | 1994 | 8.4487124869835 | | 1993 | 11.746737017495 | | 1992 | 11.383437051221 | | 1991 | 12.185630721439 | | 1990 | 21.495252052759 | | 1989 | 11.567536089056 | | 1988 | 13.991548900207 | | 1987 | 7.7171656055927 | | 1986 | 7.9763619357063 | | 1985 | 1.4811801223543 | | 1984 | 16.638253747922 | | 1983 | 13.9643880065 | | 1982 | 10.825749167569 | | 1981 | 17.96899549601 | | 1980 | 26.145410101447 | | 1979 | 10.731921430873 | | 1978 | 12.141597276466 | | 1977 | 1.2248795880284 | | 1976 | 1.3295186805823 | | 1975 | 6.6259925532098 | | 1974 | 12.302886795247 | | 1973 | 9.6266431017112 | | 1972 | 6.3494860501361 | | 1971 | 2.6653802085999 | | 1970 | 5.8669560776597 | | 1969 | 7.4569527337258 | | 1968 | 5.8605664489858 | | 1967 | 2.1892393320352 | | 1966 | 0.15560165997385 | | 1965 | 0.22278330625402 | | 1964 | 3.1956471760459 | | 1963 | 2.2729053999621 | | 1962 | 1.5035799525155 | | 1961 | 1.1344436397999 | | 1960 | -1.544676806092 |
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