| Year | Value | | 2021 | 10.009321778007 | | 2020 | 10.120102364917 | | 2019 | 10.093599965375 | | 2018 | 10.077009073484 | | 2017 | 10.078150567343 | | 2016 | 10.091091716121 | | 2015 | 10.08343408783 | | 2014 | 10.109676514254 | | 2013 | 10.197092851213 | | 2012 | 10.199873820701 | | 2011 | 10.200569812799 | | 2010 | 10.218082679913 | | 2009 | 10.25499075969 | | 2008 | 10.261800109337 | | 2007 | 10.271524600013 | | 2006 | 10.278274162942 | | 2005 | 10.259065167887 | | 2004 | 10.26795824781 | | 2003 | 10.280057015302 | | 2002 | 10.313338894408 | | 2001 | 10.342633891296 | | 2000 | 10.323925354841 | | 1999 | 10.370238432579 | | 1998 | 10.442465759074 | | 1997 | 10.495507186602 | | 1996 | 10.632763426569 | | 1995 | 10.679322645496 | | 1994 | 10.604534476578 | | 1993 | 10.368471554542 | | 1992 | 10.273026957383 | | 1991 | 10.310007627244 | | 1990 | 10.197253832413 | | 1989 | 10.336870044643 | | 1988 | 10.175850151951 | | 1987 | 10.08639979276 | | 1986 | 10.222710190885 | | 1985 | 10.23152951248 | | 1984 | 10.178879748153 | | 1983 | 9.9801941424347 | | 1982 | 9.8395748305472 | | 1981 | 9.7307096538187 | | 1980 | 9.6293807715961 | | 1979 | 9.5357855088112 | | 1978 | 9.4945355191257 | | 1977 | 9.3579234972678 | | 1976 | 9.3478040882413 | | 1975 | 9.3326249747015 | | 1974 | 9.2440801457195 | | 1973 | 9.1783039870472 | | 1972 | 9.1833636915604 | | 1971 | 9.0290427039061 | | 1970 | 9.0037441813398 | | 1969 | 9.1074681238616 | | 1968 | 9.0998785670917 | | 1967 | 9.1934831005869 | | 1966 | 9.3857518720907 | | 1965 | 9.5552519732848 | | 1964 | 9.7095729609391 | | 1963 | 9.8132969034608 | | 1962 | 10.06122242461 | | 1961 | 10.020744788504 |
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