Year | Value | 2021 | 22.295321637427 | 2020 | 21.944444444444 | 2019 | 21.597222222222 | 2018 | 21.24634502924 | 2017 | 20.895467836257 | 2016 | 20.548245614035 | 2015 | 20.197368421053 | 2014 | 19.84649122807 | 2013 | 19.499269005848 | 2012 | 19.148391812866 | 2011 | 18.797514619883 | 2010 | 18.450292397661 | 2009 | 18.099415204678 | 2008 | 17.752192982456 | 2007 | 17.401315789474 | 2006 | 17.050438596491 | 2005 | 16.703216374269 | 2004 | 16.352339181286 | 2003 | 16.001461988304 | 2002 | 15.654239766082 | 2001 | 15.303362573099 | 2000 | 14.952485380117 | 1999 | 14.605263157895 | 1998 | 14.254385964912 | 1997 | 13.815789473684 | 1996 | 12.719298245614 | 1995 | 12.353801169591 | 1994 | 12.284356725146 | 1993 | 12.536549707602 | 1992 | 12.627923976608 | 1991 | 12.719298245614 | 1990 | 12.81067251462 | 1989 | 12.902046783626 | 1988 | 12.770467836257 | 1987 | 11.239035087719 | 1986 | 11.056286549708 | 1985 | 10.891812865497 | 1984 | 10.709064327485 | 1983 | 10.544590643275 | 1982 | 10.380116959064 | 1981 | 10.197368421053 | 1980 | 10.032894736842 | 1979 | 9.8684210526316 | 1978 | 9.6856725146199 | 1977 | 9.5029239766082 | 1976 | 9.3201754385965 | 1975 | 9.1593567251462 | 1974 | 8.8925438596491 | 1973 | 8.6001461988304 | 1972 | 8.3406432748538 | 1971 | 8.0409356725146 | 1970 | 8.0994152046784 | 1969 | 8.0482456140351 | 1968 | 8.0043859649123 | 1967 | 7.9678362573099 | 1966 | 7.9312865497076 | 1965 | 7.891081871345 | 1964 | 7.8545321637427 | 1963 | 7.8362573099415 | 1962 | 7.7997076023392 | 1961 | 7.7631578947368 |
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