| Year | Value | | 2021 | 62.428927004412 | | 2020 | 62.760997886699 | | 2019 | 62.908711116762 | | 2018 | 62.710181470071 | | 2017 | 62.544188114681 | | 2016 | 62.121213019746 | | 2015 | 62.011941521393 | | 2014 | 61.766413035288 | | 2013 | 61.5728434476 | | 2012 | 61.233604415209 | | 2011 | 61.052866135342 | | 2010 | 60.646829019053 | | 2009 | 60.303610097461 | | 2008 | 59.967363797201 | | 2007 | 59.631927927293 | | 2006 | 59.278716828382 | | 2005 | 58.335077943009 | | 2004 | 58.27588732317 | | 2003 | 57.855789778056 | | 2002 | 57.515706170348 | | 2001 | 57.187730726229 | | 2000 | 56.963914724166 | | 1999 | 56.638488314591 | | 1998 | 56.20122262239 | | 1997 | 56.031011430905 | | 1996 | 55.894239957833 | | 1995 | 55.696258662693 | | 1994 | 55.924503399734 | | 1993 | 56.08393114696 | | 1992 | 56.360331979368 | | 1991 | 56.712232385606 | | 1990 | 56.957878616125 | | 1989 | 56.775881005486 | | 1988 | 56.624639959691 | | 1987 | 56.35735639464 | | 1986 | 56.401747687267 | | 1985 | 56.557325755162 | | 1984 | 56.744369867114 | | 1983 | 56.496290627634 | | 1982 | 56.104782736021 | | 1981 | 55.827841610943 | | 1980 | 55.198160364496 | | 1979 | 54.737288405563 | | 1978 | 54.324392459316 | | 1977 | 53.835997985814 | | 1976 | 53.294404529774 | | 1975 | 52.6525882438 | | 1974 | 52.111391072249 | | 1973 | 51.750954534886 | | 1972 | 51.290802842571 | | 1971 | 49.742626918199 | | 1970 | 50.208975149907 | | 1969 | 49.456175962766 | | 1968 | 48.882337762335 | | 1967 | 48.002872659525 | | 1966 | 47.61260165261 | | 1965 | 46.909929542274 | | 1964 | 46.314467311807 | | 1963 | 45.663154845896 | | 1962 | 44.882786741764 | | 1961 | 44.357139822627 | | 1960 | 43.763544836349 |
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