| Year | Value | | 2022 | 40.442529347974 | | 2021 | 40.705113533023 | | 2020 | 40.912380988959 | | 2019 | 41.116183025036 | | 2018 | 41.37042384361 | | 2017 | 41.628710033294 | | 2016 | 41.876744617857 | | 2015 | 42.153846867722 | | 2014 | 42.492739168208 | | 2013 | 42.822026178969 | | 2012 | 43.135778648844 | | 2011 | 43.362004870533 | | 2010 | 43.619582444355 | | 2009 | 44.003243057178 | | 2008 | 44.440707605812 | | 2007 | 44.880331744865 | | 2006 | 45.165699618285 | | 2005 | 45.564776932793 | | 2004 | 45.904477531363 | | 2003 | 46.169837888301 | | 2002 | 46.433567241306 | | 2001 | 46.68819885076 | | 2000 | 46.944002620446 | | 1999 | 47.189474066627 | | 1998 | 47.437998959907 | | 1997 | 47.683825277712 | | 1996 | 47.908076112039 | | 1995 | 48.101496415201 | | 1994 | 48.297585830391 | | 1993 | 48.565191070459 | | 1992 | 48.980973293895 | | 1991 | 49.528824779973 | | 1990 | 49.925587919861 | | 1989 | 50.404915328082 | | 1988 | 50.900198077134 | | 1987 | 51.424832261327 | | 1986 | 51.994680688589 | | 1985 | 52.610337605919 | | 1984 | 53.223533015512 | | 1983 | 53.861223056846 | | 1982 | 54.428833781378 | | 1981 | 54.965678166888 | | 1980 | 55.516207741965 | | 1979 | 56.028232808622 | | 1978 | 56.45818833103 | | 1977 | 56.93392509834 | | 1976 | 57.555534261655 | | 1975 | 58.201249114054 | | 1974 | 58.802270098119 | | 1973 | 59.433762300037 | | 1972 | 60.128908507035 | | 1971 | 60.830999296744 | | 1970 | 61.518451605283 | | 1969 | 62.232887124936 | | 1968 | 62.942951144995 | | 1967 | 63.642371868087 | | 1966 | 64.326746091103 | | 1965 | 65.117014900158 | | 1964 | 65.946206795186 | | 1963 | 66.738507332175 | | 1962 | 67.505168219065 | | 1961 | 68.245322549914 | | 1960 | 68.977838123875 |
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