| Year | Value | | 2021 | 44.616391962068 | | 2020 | 44.616391962068 | | 2019 | 44.377624745992 | | 2018 | 44.13795439151 | | 2017 | 43.898284037029 | | 2016 | 43.658613682547 | | 2015 | 43.418943328065 | | 2014 | 43.179272973583 | | 2013 | 42.939602619101 | | 2012 | 42.331896590652 | | 2011 | 42.460261910138 | | 2010 | 42.220591555656 | | 2009 | 41.980921201174 | | 2008 | 41.741250846692 | | 2007 | 41.11356965455 | | 2006 | 40.495935877173 | | 2005 | 39.867012869722 | | 2004 | 39.238089862271 | | 2003 | 38.688191465342 | | 2002 | 38.609166854821 | | 2001 | 38.496274554075 | | 2000 | 38.38338225333 | | 1999 | 38.270489952585 | | 1998 | 38.15759765184 | | 1997 | 38.048092120117 | | 1996 | 37.730853465794 | | 1995 | 37.310894107022 | | 1994 | 36.89093474825 | | 1993 | 36.470975389478 | | 1992 | 36.051016030707 | | 1991 | 35.631056671935 | | 1990 | 35.211097313163 | | 1989 | 36.125536238429 | | 1988 | 36.125536238429 | | 1987 | 36.125536238429 | | 1986 | 36.125536238429 | | 1985 | 36.125536238429 | | 1984 | 34.996613230978 | | 1983 | 34.996613230978 | | 1982 | 34.996613230978 | | 1981 | 34.996613230978 | | 1980 | 33.867690223527 | | 1979 | 33.867690223527 | | 1978 | 33.867690223527 | | 1977 | 32.738767216076 | | 1976 | 32.738767216076 | | 1975 | 32.738767216076 | | 1974 | 32.738767216076 | | 1973 | 32.738767216076 | | 1972 | 32.738767216076 | | 1971 | 32.738767216076 | | 1970 | 31.609844208625 | | 1969 | 30.480921201174 | | 1968 | 30.480921201174 | | 1967 | 30.480921201174 | | 1966 | 30.480921201174 | | 1965 | 30.480921201174 | | 1964 | 30.480921201174 | | 1963 | 30.480921201174 | | 1962 | 29.351998193723 | | 1961 | 29.351998193723 |
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