| Year | Value | | 2021 | 46.56432748538 | | 2020 | 46.103801169591 | | 2019 | 45.756578947368 | | 2018 | 45.369152046784 | | 2017 | 44.652777777778 | | 2016 | 44.232456140351 | | 2015 | 43.808479532164 | | 2014 | 43.311403508772 | | 2013 | 42.854532163743 | | 2012 | 42.174707602339 | | 2011 | 41.71418128655 | | 2010 | 41.08918128655 | | 2009 | 40.614035087719 | | 2008 | 40.202850877193 | | 2007 | 39.806286549708 | | 2006 | 39.437134502924 | | 2005 | 39.046052631579 | | 2004 | 38.636695906433 | | 2003 | 38.223684210526 | | 2002 | 37.869152046784 | | 2001 | 37.510964912281 | | 2000 | 37.145467836257 | | 1999 | 36.790935672515 | | 1998 | 36.440058479532 | | 1997 | 36.001461988304 | | 1996 | 34.904970760234 | | 1995 | 34.53947368421 | | 1994 | 34.470029239766 | | 1993 | 34.722222222222 | | 1992 | 34.813596491228 | | 1991 | 34.904970760234 | | 1990 | 34.99634502924 | | 1989 | 35.087719298246 | | 1988 | 34.956140350877 | | 1987 | 33.406432748538 | | 1986 | 33.205409356725 | | 1985 | 33.022660818713 | | 1984 | 32.839912280702 | | 1983 | 32.65716374269 | | 1982 | 32.474415204678 | | 1981 | 32.291666666667 | | 1980 | 32.108918128655 | | 1979 | 31.926169590643 | | 1978 | 31.743421052632 | | 1977 | 31.56067251462 | | 1976 | 31.377923976608 | | 1975 | 31.198830409357 | | 1974 | 30.895467836257 | | 1973 | 30.603070175439 | | 1972 | 30.343567251462 | | 1971 | 30.043859649123 | | 1970 | 30.102339181286 | | 1969 | 30.051169590643 | | 1968 | 30.007309941521 | | 1967 | 29.970760233918 | | 1966 | 29.934210526316 | | 1965 | 29.894005847953 | | 1964 | 29.857456140351 | | 1963 | 29.820906432749 | | 1962 | 29.784356725146 | | 1961 | 29.747807017544 |
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