| Year | Value | | 2021 | 10.795379054534 | | 2020 | 10.763014498192 | | 2019 | 10.738604892069 | | 2018 | 10.751380279469 | | 2017 | 10.750842448317 | | 2016 | 10.73075128728 | | 2015 | 10.714988311402 | | 2014 | 10.692646762259 | | 2013 | 10.675257358281 | | 2012 | 10.655801279191 | | 2011 | 10.629363298334 | | 2010 | 10.567794181977 | | 2009 | 10.571116389473 | | 2008 | 10.52817819441 | | 2007 | 10.532760897635 | | 2006 | 10.54379953832 | | 2005 | 10.548460919422 | | 2004 | 10.529330353401 | | 2003 | 10.521541372953 | | 2002 | 10.495125925933 | | 2001 | 10.51295733177 | | 2000 | 10.508081614935 | | 1999 | 10.53233522582 | | 1998 | 10.520465518341 | | 1997 | 10.524657937757 | | 1996 | 10.492754979088 | | 1995 | 10.499125686526 | | 1994 | 10.502337788453 | | 1993 | 10.528650683856 | | 1992 | 10.516681849185 | | 1991 | 10.550576634125 | | 1990 | 10.531086490573 | | 1989 | 10.526368732796 | | 1988 | 10.517071683814 | | 1987 | 10.534619219493 | | 1986 | 10.533858508682 | | 1985 | 10.532427432183 | | 1984 | 10.421594047645 | | 1983 | 10.280501061826 | | 1982 | 10.238335097476 | | 1981 | 10.14961818851 | | 1980 | 10.123792914511 | | 1979 | 10.103495575713 | | 1978 | 10.052850215636 | | 1977 | 9.9532723593238 | | 1976 | 9.9069016299744 | | 1975 | 9.8573979710285 | | 1974 | 9.8554528517527 | | 1973 | 9.8454014206179 | | 1972 | 9.8333357985207 | | 1971 | 9.7861441255358 | | 1970 | 9.8205967393438 | | 1969 | 9.8369673801124 | | 1968 | 9.7721113245811 | | 1967 | 9.6641482412571 | | 1966 | 9.6474811675283 | | 1965 | 9.6297997527457 | | 1964 | 9.5973686068581 | | 1963 | 9.575964714292 | | 1962 | 9.5076494915413 | | 1961 | 9.5001817876549 |
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