Year | Value | 2021 | 18.333333333333 | 2020 | 18.333333333333 | 2019 | 18.333333333333 | 2018 | 18.333333333333 | 2017 | 19.292929292929 | 2016 | 20.151515151515 | 2015 | 20 | 2014 | 21.060606060606 | 2013 | 21.262626262626 | 2012 | 22.020202020202 | 2011 | 22.272727272727 | 2010 | 21.767676767677 | 2009 | 20.707070707071 | 2008 | 18.686868686869 | 2007 | 17.171717171717 | 2006 | 18.181818181818 | 2005 | 19.191919191919 | 2004 | 18.686868686869 | 2003 | 18.181818181818 | 2002 | 18.181818181818 | 2001 | 18.686868686869 | 2000 | 19.69696969697 | 1999 | 19.69696969697 | 1998 | 18.686868686869 | 1997 | 17.676767676768 | 1996 | 18.181818181818 | 1995 | 18.181818181818 | 1994 | 18.181818181818 | 1993 | 18.181818181818 | 1992 | 18.686868686869 | 1991 | 18.686868686869 | 1990 | 18.686868686869 | 1989 | 18.686868686869 | 1988 | 18.686868686869 | 1987 | 19.191919191919 | 1986 | 19.191919191919 | 1985 | 19.191919191919 | 1984 | 19.191919191919 | 1983 | 19.191919191919 | 1982 | 19.69696969697 | 1981 | 19.69696969697 | 1980 | 19.69696969697 | 1979 | 19.69696969697 | 1978 | 19.69696969697 | 1977 | 20.20202020202 | 1976 | 20.20202020202 | 1975 | 20.20202020202 | 1974 | 20.20202020202 | 1973 | 20.20202020202 | 1972 | 20.707070707071 | 1971 | 20.707070707071 | 1970 | 20.707070707071 | 1969 | 20.707070707071 | 1968 | 20.20202020202 | 1967 | 20.20202020202 | 1966 | 20.20202020202 | 1965 | 20.20202020202 | 1964 | 20.20202020202 | 1963 | 20.20202020202 | 1962 | 20.20202020202 | 1961 | 20.20202020202 |
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