| Year | Value | | 2022 | 50.124472783642 | | 2021 | 50.12898812396 | | 2020 | 50.131804708504 | | 2019 | 50.138395113151 | | 2018 | 50.148103340517 | | 2017 | 50.158870218689 | | 2016 | 50.172459674852 | | 2015 | 50.184555048559 | | 2014 | 50.195427403694 | | 2013 | 50.207804334612 | | 2012 | 50.220908563073 | | 2011 | 50.233697475651 | | 2010 | 50.24598506613 | | 2009 | 50.258524207483 | | 2008 | 50.27145593077 | | 2007 | 50.284601037505 | | 2006 | 50.29821140756 | | 2005 | 50.312491841615 | | 2004 | 50.326379746769 | | 2003 | 50.340026241375 | | 2002 | 50.354212536822 | | 2001 | 50.36661442242 | | 2000 | 50.377097343064 | | 1999 | 50.386295695624 | | 1998 | 50.395466893624 | | 1997 | 50.405593328141 | | 1996 | 50.416284723665 | | 1995 | 50.428088186128 | | 1994 | 50.441626659233 | | 1993 | 50.458040680326 | | 1992 | 50.475627697961 | | 1991 | 50.49386897412 | | 1990 | 50.514858466631 | | 1989 | 50.538703256189 | | 1988 | 50.564720365762 | | 1987 | 50.593109674662 | | 1986 | 50.625222986673 | | 1985 | 50.660142015904 | | 1984 | 50.694499803861 | | 1983 | 50.726841078225 | | 1982 | 50.754229088008 | | 1981 | 50.783221475294 | | 1980 | 50.819687716662 | | 1979 | 50.853564018727 | | 1978 | 50.884226045293 | | 1977 | 50.915481622327 | | 1976 | 50.946732494273 | | 1975 | 50.980700425567 | | 1974 | 51.018270818076 | | 1973 | 51.056983823254 | | 1972 | 51.096561434755 | | 1971 | 51.138011422363 | | 1970 | 51.181822676 | | 1969 | 51.226521706485 | | 1968 | 51.270867426569 | | 1967 | 51.315771636463 | | 1966 | 51.361144370607 | | 1965 | 51.406780143569 | | 1964 | 51.4528881113 | | 1963 | 51.498780932917 | | 1962 | 51.543588882095 | | 1961 | 51.455679468036 | | 1960 | 51.22350129201 |
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