| Year | Value | | 2022 | 1.5637247147538 | | 2021 | 1.5141638304309 | | 2020 | 1.5424437091958 | | 2019 | 1.3825483836327 | | 2018 | 1.3482899932307 | | 2017 | 1.3341323965999 | | 2016 | 1.3280952835887 | | 2015 | 1.3123100339722 | | 2014 | 1.3261264183664 | | 2013 | 1.3562378617029 | | 2012 | 1.4046474734155 | | 2011 | 1.4069478586779 | | 2010 | 1.4695572778457 | | 2009 | 1.5347256153516 | | 2008 | 1.4577435397032 | | 2007 | 1.4388638994641 | | 2006 | 1.4791623409178 | | 2005 | 1.483683382976 | | 2004 | 1.5637717449352 | | 2003 | 1.5888691648157 | | 2002 | 1.5942687849268 | | 2001 | 1.6105374071609 | | 2000 | 1.6544683397497 | | 1999 | 1.6918582778097 | | 1998 | 1.7180724491423 | | 1997 | 1.7613118893002 | | 1996 | 1.7959635039682 | | 1995 | 1.8131797705536 | | 1994 | 1.927759887436 | | 1993 | 2.0113115023412 | | 1992 | 2.0792401821513 | | 1991 | 2.1873037460362 | | 1990 | 2.378149303897 | | 1989 | 2.4479821149166 | | 1988 | 2.532270222543 | | 1987 | 2.631061783824 | | 1986 | 2.6071700483701 | | 1985 | 2.6804306926731 | | 1984 | 2.7350362312616 | | 1983 | 2.8043513043684 | | 1982 | 2.8305293628315 | | 1981 | 2.7987736277418 | | 1980 | 2.7198090810076 | | 1979 | 2.7653700092454 | | 1978 | 2.7949440338952 | | 1977 | 2.812044896706 | | 1976 | 2.7950859399941 | | 1975 | 2.8703382511216 | | 1974 | 2.8332911735175 | | 1973 | 2.8061811908024 | | 1972 | 2.9013286026665 | | 1971 | 2.8609716290351 | | 1970 | 2.8578255920063 | | 1969 | 3.0346852224706 | | 1968 | 3.2691706228809 | | 1967 | 3.3089727117595 | | 1966 | 3.36116538905 | | 1965 | 3.3657546528549 | | 1964 | 3.4801148957098 | | 1963 | 3.5654516083462 | | 1962 | 3.736747537333 | | 1961 | 3.710953607796 | | 1960 | 3.8014852952234 |
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