| Year | Value | | 2022 | 50.371102619532 | | 2021 | 50.351723158553 | | 2020 | 50.330961807301 | | 2019 | 50.31378201368 | | 2018 | 50.300322172384 | | 2017 | 50.285945552583 | | 2016 | 50.273488386638 | | 2015 | 50.263103236841 | | 2014 | 50.250786836749 | | 2013 | 50.241676640052 | | 2012 | 50.235723260159 | | 2011 | 50.22966211968 | | 2010 | 50.226120785597 | | 2009 | 50.225002025296 | | 2008 | 50.225397163394 | | 2007 | 50.223995487728 | | 2006 | 50.225102633341 | | 2005 | 50.228016479291 | | 2004 | 50.232962231159 | | 2003 | 50.241626168294 | | 2002 | 50.252493572027 | | 2001 | 50.266365334622 | | 2000 | 50.280513130818 | | 1999 | 50.293659321824 | | 1998 | 50.308236919358 | | 1997 | 50.324804652988 | | 1996 | 50.339021700181 | | 1995 | 50.3509265127 | | 1994 | 50.361921931362 | | 1993 | 50.371627093521 | | 1992 | 50.361121764065 | | 1991 | 50.344379901387 | | 1990 | 50.344870602055 | | 1989 | 50.353096502809 | | 1988 | 50.363542502441 | | 1987 | 50.374774471999 | | 1986 | 50.385353275856 | | 1985 | 50.395673668423 | | 1984 | 50.406116873737 | | 1983 | 50.416070661308 | | 1982 | 50.427191574442 | | 1981 | 50.43683858946 | | 1980 | 50.444741315743 | | 1979 | 50.45203000766 | | 1978 | 50.458112597647 | | 1977 | 50.462496493245 | | 1976 | 50.467937759481 | | 1975 | 50.475592332991 | | 1974 | 50.483047615067 | | 1973 | 50.487517411336 | | 1972 | 50.490819080819 | | 1971 | 50.496352731399 | | 1970 | 50.502496900519 | | 1969 | 50.505945786247 | | 1968 | 50.505999937337 | | 1967 | 50.505909150931 | | 1966 | 50.506642059996 | | 1965 | 50.504725480822 | | 1964 | 50.501724221672 | | 1963 | 50.497593938773 | | 1962 | 50.492901784756 | | 1961 | 50.48616556514 | | 1960 | 50.48173144054 |
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