| Year | Value | | 2024 | 51.506119771797 | | 2023 | 51.49818991495 | | 2022 | 51.481060053929 | | 2021 | 51.44481610497 | | 2020 | 51.391218175877 | | 2019 | 51.349365268708 | | 2018 | 51.321160369061 | | 2017 | 51.29068295325 | | 2016 | 51.253594336586 | | 2015 | 51.214267355127 | | 2014 | 51.181953695903 | | 2013 | 51.162318717553 | | 2012 | 51.149465501132 | | 2011 | 51.142517325749 | | 2010 | 51.143027617562 | | 2009 | 51.147435447629 | | 2008 | 51.15621312094 | | 2007 | 51.166079028183 | | 2006 | 51.173618169598 | | 2005 | 51.177580842249 | | 2004 | 51.18003616506 | | 2003 | 51.181769797498 | | 2002 | 51.183012583213 | | 2001 | 51.184022145894 | | 2000 | 51.169001315197 | | 1999 | 51.139378011627 | | 1998 | 51.111517934257 | | 1997 | 51.083332720883 | | 1996 | 51.054076277836 | | 1995 | 51.023405112963 | | 1994 | 50.990646847011 | | 1993 | 50.955939654737 | | 1992 | 50.920680747624 | | 1991 | 50.885577323816 | | 1990 | 50.847367867602 | | 1989 | 50.791468681338 | | 1988 | 50.720413052024 | | 1987 | 50.647575105311 | | 1986 | 50.571707068259 | | 1985 | 50.492492252551 | | 1984 | 50.409606060235 | | 1983 | 50.322332221561 | | 1982 | 50.230392573054 | | 1981 | 50.134671448869 | | 1980 | 50.078248496088 | | 1979 | 50.064482454274 | | 1978 | 50.052503127352 | | 1977 | 50.042162790839 | | 1976 | 50.033028000489 |
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