| Year | Value | | 2021 | 32.343723990597 | | 2020 | 32.345294103297 | | 2019 | 32.345950295298 | | 2018 | 32.350914527583 | | 2017 | 32.345799439349 | | 2016 | 32.319825362365 | | 2015 | 32.262595208608 | | 2014 | 32.316285211338 | | 2013 | 32.238984846879 | | 2012 | 32.370513556491 | | 2011 | 32.385303645765 | | 2010 | 32.352536573657 | | 2009 | 32.371041400973 | | 2008 | 32.318506505456 | | 2007 | 32.271049205957 | | 2006 | 32.279925655911 | | 2005 | 32.257209370794 | | 2004 | 32.204464402068 | | 2003 | 32.188435618047 | | 2002 | 32.151441498981 | | 2001 | 32.213874621121 | | 2000 | 32.283385954032 | | 1999 | 32.241972546666 | | 1998 | 32.229104947042 | | 1997 | 32.24606136585 | | 1996 | 32.246899934122 | | 1995 | 32.221250629539 | | 1994 | 32.214572952385 | | 1993 | 32.172329923915 | | 1992 | 32.104202209829 | | 1991 | 32.109246408888 | | 1990 | 32.117111309842 | | 1989 | 32.096954392796 | | 1988 | 32.113801250375 | | 1987 | 32.104904565453 | | 1986 | 32.073968832004 | | 1985 | 32.06251823668 | | 1984 | 32.045804665979 | | 1983 | 32.027622369349 | | 1982 | 32.047188409794 | | 1981 | 32.052271139862 | | 1980 | 32.050663007363 | | 1979 | 32.093529398326 | | 1978 | 32.129780425376 | | 1977 | 32.129600227481 | | 1976 | 32.150634221526 | | 1975 | 32.133156331159 | | 1974 | 32.233561561679 | | 1973 | 32.269586879767 | | 1972 | 32.251553821336 | | 1971 | 32.236458274685 | | 1970 | 32.254205741693 | | 1969 | 32.308264118212 | | 1968 | 32.323359664863 | | 1967 | 32.333967346293 | | 1966 | 32.319687775137 | | 1965 | 32.303368265244 | | 1964 | 32.300063564491 | | 1963 | 32.288639907566 | | 1962 | 32.279664177125 | | 1961 | 32.26987247119 |
|