| Year | Value | | 2021 | 12.615985674752 | | 2020 | 12.615985674752 | | 2019 | 12.615985674752 | | 2018 | 12.615985674752 | | 2017 | 12.615985674752 | | 2016 | 12.615985674752 | | 2015 | 12.615985674752 | | 2014 | 12.615985674752 | | 2013 | 12.615985674752 | | 2012 | 12.209018394921 | | 2011 | 11.80205111509 | | 2010 | 11.80205111509 | | 2009 | 11.598567475175 | | 2008 | 11.598567475175 | | 2007 | 11.39508383526 | | 2006 | 11.191600195344 | | 2005 | 11.15497314016 | | 2004 | 11.163112485756 | | 2003 | 11.159042812958 | | 2002 | 11.15497314016 | | 2001 | 11.150903467361 | | 2000 | 11.146833794563 | | 1999 | 11.142764121765 | | 1998 | 11.138694448966 | | 1997 | 11.134624776168 | | 1996 | 11.13055510337 | | 1995 | 11.126485430571 | | 1994 | 11.224157577731 | | 1993 | 11.32182972489 | | 1992 | 11.415432199251 | | 1991 | 11.513104346411 | | 1990 | 11.61077649357 | | 1989 | 11.708448640729 | | 1988 | 11.806120787889 | | 1987 | 11.89972326225 | | 1986 | 11.997395409409 | | 1985 | 12.095067556568 | | 1984 | 12.192739703728 | | 1983 | 12.286342178089 | | 1982 | 12.384014325248 | | 1981 | 12.481686472408 | | 1980 | 12.579358619567 | | 1979 | 12.677030766726 | | 1978 | 12.770633241087 | | 1977 | 12.868305388247 | | 1976 | 12.965977535406 | | 1975 | 13.063649682566 | | 1974 | 13.161321829725 | | 1973 | 13.254924304086 | | 1972 | 13.352596451245 | | 1971 | 13.450268598405 | | 1970 | 13.547940745564 | | 1969 | 13.641543219925 | | 1968 | 13.739215367084 | | 1967 | 13.836887514244 | | 1966 | 13.934559661403 | | 1965 | 14.032231808563 | | 1964 | 14.125834282924 | | 1963 | 14.223506430083 | | 1962 | 14.321178577242 | | 1961 | 14.325248250041 |
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