| Year | Value | | 2022 | 50.821077693238 | | 2021 | 50.837271697344 | | 2020 | 50.858681976038 | | 2019 | 50.873535485549 | | 2018 | 50.884117525181 | | 2017 | 50.895034653132 | | 2016 | 50.90202554938 | | 2015 | 50.904136692063 | | 2014 | 50.901912828264 | | 2013 | 50.890731581164 | | 2012 | 50.874024785531 | | 2011 | 50.859319906678 | | 2010 | 50.844736455458 | | 2009 | 50.830367029057 | | 2008 | 50.816138123963 | | 2007 | 50.802010987845 | | 2006 | 50.788337469005 | | 2005 | 50.775050648999 | | 2004 | 50.760901497202 | | 2003 | 50.743629021562 | | 2002 | 50.724932349142 | | 2001 | 50.703363957453 | | 2000 | 50.674696657261 | | 1999 | 50.639136898796 | | 1998 | 50.593433522726 | | 1997 | 50.538687398905 | | 1996 | 50.48442215192 | | 1995 | 50.437726124711 | | 1994 | 50.401170393669 | | 1993 | 50.372967849526 | | 1992 | 50.347155952074 | | 1991 | 50.319739179182 | | 1990 | 50.288528358741 | | 1989 | 50.254157702608 | | 1988 | 50.218495857815 | | 1987 | 50.183455847077 | | 1986 | 50.147439570191 | | 1985 | 50.102251213634 | | 1984 | 50.041778352868 | | 1983 | 49.970819235778 | | 1982 | 49.895263158595 | | 1981 | 49.811919934095 | | 1980 | 49.718270177664 | | 1979 | 49.614482878346 | | 1978 | 49.501373493643 | | 1977 | 49.383973805535 | | 1976 | 49.289903198007 | | 1975 | 49.235665685801 | | 1974 | 49.215654695454 | | 1973 | 49.228118211104 | | 1972 | 49.261069284844 | | 1971 | 49.304386060068 | | 1970 | 49.356670171146 | | 1969 | 49.419539767769 | | 1968 | 49.490790762421 | | 1967 | 49.566656636323 | | 1966 | 49.643997388971 | | 1965 | 49.720993064207 | | 1964 | 49.794725152738 | | 1963 | 49.863900570082 | | 1962 | 49.935672453836 | | 1961 | 50.011077841288 | | 1960 | 50.088614211819 |
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