| Year | Value | | 2022 | 8.3337063009623 | | 2021 | 4.271663815368 | | 2020 | 2.0024120575929 | | 2019 | 2.2521219135803 | | 2018 | 1.5091542302474 | | 2017 | 2.9949004580944 | | 2016 | 3.5571766355628 | | 2015 | 3.3980919474631 | | 2014 | 3.4119457980747 | | 2013 | 2.76789666082 | | 2012 | 3.6112129494016 | | 2011 | 3.3693109533385 | | 2010 | 1.528320597329 | | 2009 | 2.936231535967 | | 2008 | 5.7858759820675 | | 2007 | 1.7799864468037 | | 2006 | 2.0022580124882 | | 2005 | 1.6163019386254 | | 2004 | 3.6624732009223 | | 2003 | 2.2593775336307 | | 2002 | 0.19313500385372 | | 2001 | 1.9770987850205 | | 2000 | 3.7573383334447 | | 1999 | 3.4696599629302 | | 1998 | 7.2478217521347 | | 1997 | 8.5621894895365 | | 1996 | 11.537942411518 | | 1995 | 11.128702970709 | | 1994 | 23.736905056505 | | 1993 | 48.579986446888 | | 1992 | 73.528294244264 | | 1991 | 409.53016662202 | | 1990 | 7,481.6636112453 | | 1989 | 3,398.6790100533 | | 1988 | 667.01932858596 | | 1987 | 85.822306238185 | | 1986 | 77.92102554736 | | 1985 | 163.39950524369 | | 1984 | 110.20851956254 | | 1983 | 111.15063520916 | | 1982 | 64.448158538793 | | 1981 | 75.433268757606 | | 1980 | 59.145071244491 | | 1979 | 66.694422966488 | | 1978 | 57.84878262515 | | 1977 | 38.054091419679 | | 1976 | 33.483275663457 | | 1975 | 23.618735296333 | | 1974 | 16.89166666657 | | 1973 | 9.489051095034 | | 1972 | 7.2197221677055 | | 1971 | 6.7906393649542 | | 1970 | 5.0252359007242 | | 1969 | 6.2361580607806 | | 1968 | 19.086618545438 | | 1967 | 9.7836025606341 | | 1966 | 8.8406037492221 | | 1965 | 16.389961389442 | | 1964 | 9.7922848666348 | | 1963 | 6.0701438842859 | | 1962 | 6.6410932635975 | | 1961 | 5.9167089883637 | | 1960 | 8.6644591627191 |
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