| Year | Value | | 2022 | 50.464281558664 | | 2021 | 50.444928525873 | | 2020 | 50.424580745695 | | 2019 | 50.404025361729 | | 2018 | 50.385678135625 | | 2017 | 50.369138318871 | | 2016 | 50.352809713857 | | 2015 | 50.338056810659 | | 2014 | 50.325044128635 | | 2013 | 50.313267270923 | | 2012 | 50.303758040603 | | 2011 | 50.295530218462 | | 2010 | 50.311870103059 | | 2009 | 50.331108813214 | | 2008 | 50.328424948202 | | 2007 | 50.326446959109 | | 2006 | 50.325103212851 | | 2005 | 50.324707250958 | | 2004 | 50.32911383365 | | 2003 | 50.335765744144 | | 2002 | 50.341463290734 | | 2001 | 50.348859831987 | | 2000 | 50.357819317064 | | 1999 | 50.368092546895 | | 1998 | 50.380590445529 | | 1997 | 50.396024243061 | | 1996 | 50.412947892136 | | 1995 | 50.431593498945 | | 1994 | 50.453901775974 | | 1993 | 50.477733278518 | | 1992 | 50.501444673582 | | 1991 | 50.525052522235 | | 1990 | 50.552803902081 | | 1989 | 50.584162138841 | | 1988 | 50.614714101321 | | 1987 | 50.646070147744 | | 1986 | 50.67682891727 | | 1985 | 50.7086578116 | | 1984 | 50.745057298022 | | 1983 | 50.783336854104 | | 1982 | 50.820918579495 | | 1981 | 50.8582084953 | | 1980 | 50.895571128926 | | 1979 | 50.930790512213 | | 1978 | 50.962197533943 | | 1977 | 50.992058908 | | 1976 | 51.021610610718 | | 1975 | 51.04937789781 | | 1974 | 51.075188663418 | | 1973 | 51.099072805325 | | 1972 | 51.121021809283 | | 1971 | 51.14176815612 | | 1970 | 51.161764240905 | | 1969 | 51.180927294316 | | 1968 | 51.198359062881 | | 1967 | 51.214379626396 | | 1966 | 51.229109277412 | | 1965 | 51.242247940505 | | 1964 | 51.254125908021 | | 1963 | 51.269255214373 | | 1962 | 51.282082941516 | | 1961 | 51.288524539024 | | 1960 | 51.293840081064 |
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