| Year | Value | | 2022 | 9.597511728725 | | 2021 | 2.4402485114408 | | 2020 | 0.74079181222034 | | 2019 | 1.4368195699643 | | 2018 | 2.0531649986519 | | 2017 | 2.1259708600261 | | 2016 | 1.9738526465318 | | 2015 | 0.56142915279007 | | 2014 | 0.34000283335692 | | 2013 | 1.1130959402754 | | 2012 | 2.839663434459 | | 2011 | 3.5320821072274 | | 2010 | 2.1892992042246 | | 2009 | 0.053145674125377 | | 2008 | 4.489444205084 | | 2007 | 1.8230563002681 | | 2006 | 1.7912077007046 | | 2005 | 2.7814326367002 | | 2004 | 2.0972831123931 | | 2003 | 1.5889639997038 | | 2002 | 1.6452143617536 | | 2001 | 2.4692582308608 | | 2000 | 2.5445177619091 | | 1999 | 1.1208482341785 | | 1998 | 0.94925028835061 | | 1997 | 1.6281604951296 | | 1996 | 2.0770210735067 | | 1995 | 1.4679669909027 | | 1994 | 2.377540844764 | | 1993 | 2.7544264347346 | | 1992 | 2.4279556716462 | | 1991 | 3.2153106926081 | | 1990 | 3.4483121796181 | | 1989 | 3.1070506511109 | | 1988 | 1.1609349341532 | | 1987 | 1.5533826131495 | | 1986 | 1.2943681910248 | | 1985 | 4.8687339949694 | | 1984 | 6.3417749100913 | | 1983 | 7.6616098374388 | | 1982 | 8.7265490655547 | | 1981 | 7.6274865681428 | | 1980 | 6.6486882965536 | | 1979 | 4.4690839490048 | | 1978 | 4.4705933159294 | | 1977 | 7.096000591326 | | 1976 | 9.0686098105497 | | 1975 | 12.768198592051 | | 1974 | 12.677887751345 | | 1973 | 6.9552800871991 | | 1972 | 5.4484312843808 | | 1971 | 4.3436285461209 | | 1970 | 3.9084723847191 | | 1969 | 3.7539922905328 | | 1968 | 2.7014498293135 | | 1967 | 2.7303026859091 | | 1966 | 4.1743476185299 | | 1965 | 4.0652013747464 | | 1964 | 4.1687605856437 | | 1963 | 2.148003413322 | | 1962 | 1.4046070354351 | | 1961 | 0.99267626076734 | | 1960 | 0.29946725476969 |
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