| Year | Value | | 2024 | 49.711410201378 | | 2023 | 49.705604624718 | | 2022 | 49.704622938714 | | 2021 | 49.702141598242 | | 2020 | 49.695635425718 | | 2019 | 49.695897927478 | | 2018 | 49.705283894296 | | 2017 | 49.715860282554 | | 2016 | 49.7645404528 | | 2015 | 49.854681965426 | | 2014 | 49.951792124267 | | 2013 | 50.054869920941 | | 2012 | 50.126901691533 | | 2011 | 50.165554983415 | | 2010 | 50.20608244825 | | 2009 | 50.245814302716 | | 2008 | 50.283248080825 | | 2007 | 50.31932517028 | | 2006 | 50.354442226826 | | 2005 | 50.388912697957 | | 2004 | 50.421212872651 | | 2003 | 50.421377400412 | | 2002 | 50.479940886312 | | 2001 | 50.623697964256 | | 2000 | 50.754924638114 | | 1999 | 50.872906156646 | | 1998 | 50.913768372639 | | 1997 | 50.879027604637 | | 1996 | 50.842404534499 | | 1995 | 50.807502033279 | | 1994 | 50.773008781645 | | 1993 | 50.740159009631 | | 1992 | 50.708537495189 | | 1991 | 50.654145703272 | | 1990 | 50.590873512132 | | 1989 | 50.545020468572 | | 1988 | 50.500609458222 | | 1987 | 50.45524426285 | | 1986 | 50.40894725507 | | 1985 | 50.362557679631 | | 1984 | 50.316044243546 | | 1983 | 50.270264382558 | | 1982 | 50.223862417714 | | 1981 | 50.172576090367 | | 1980 | 50.131025313795 | | 1979 | 50.115164845893 | | 1978 | 50.120085996053 | | 1977 | 50.142077781896 | | 1976 | 50.178128507955 | | 1975 | 50.228194638034 |
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