| Year | Value | | 2021 | 11.861239993598 | | 2020 | 11.602600052025 | | 2019 | 10.402585401226 | | 2018 | 10.510737357183 | | 2017 | 10.461536537587 | | 2016 | 10.177698945789 | | 2015 | 10.396667511123 | | 2014 | 9.8504773406439 | | 2013 | 10.009299025991 | | 2012 | 10.067555432838 | | 2011 | 9.8119565493255 | | 2010 | 9.8390592263045 | | 2009 | 9.8464361336863 | | 2008 | 9.8183793158212 | | 2007 | 9.7590374758698 | | 2006 | 9.6758345493492 | | 2005 | 9.8494701673467 | | 2004 | 9.6575107680328 | | 2003 | 10.117641402874 | | 2002 | 9.938437293286 | | 2001 | 9.8447403340614 | | 2000 | 9.9463678364768 | | 1999 | 10.118453624479 | | 1998 | 10.140058057846 | | 1997 | 10.137517389811 | | 1996 | 10.24711075232 | | 1995 | 10.244134595491 | | 1994 | 10.197519516911 | | 1993 | 10.331950688351 | | 1992 | 10.239097477706 | | 1991 | 10.355265763609 | | 1990 | 10.326223138599 | | 1989 | 10.230702477571 | | 1988 | 10.221057031373 | | 1987 | 10.248881311015 | | 1986 | 10.354821068387 | | 1985 | 10.496661748305 | | 1984 | 10.305635246244 | | 1983 | 10.444598465444 | | 1982 | 10.21335271316 | | 1981 | 10.331415866887 | | 1980 | 10.459917653125 | | 1979 | 10.253845009185 | | 1978 | 10.348684350078 | | 1977 | 10.247237475901 | | 1976 | 10.42071901895 | | 1975 | 10.461969226073 | | 1974 | 10.25556011393 | | 1973 | 10.383486729789 | | 1972 | 10.254504153342 | | 1971 | 10.452289386541 | | 1970 | 10.372946708039 | | 1969 | 10.596813108761 | | 1968 | 10.357144425158 | | 1967 | 10.091853161225 | | 1966 | 9.9512312403542 | | 1965 | 10.089241870401 | | 1964 | 9.8721762524093 | | 1963 | 10.119389190668 | | 1962 | 10.229279149433 | | 1961 | 9.8407902672109 | | 1960 | 10.050375096938 |
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