| Year | Value | | 2021 | 61.887966003221 | | 2020 | 62.385980953166 | | 2019 | 62.875735959551 | | 2018 | 62.616047812198 | | 2017 | 62.252157896849 | | 2016 | 61.855365250612 | | 2015 | 61.382626890693 | | 2014 | 61.051512584022 | | 2013 | 60.603594501562 | | 2012 | 60.335170031983 | | 2011 | 59.887382982888 | | 2010 | 59.24673657039 | | 2009 | 58.82946729609 | | 2008 | 57.959953572617 | | 2007 | 57.788849760538 | | 2006 | 57.407293756811 | | 2005 | 56.818813522995 | | 2004 | 56.362970156631 | | 2003 | 55.874386646682 | | 2002 | 55.345111443243 | | 2001 | 54.948979707195 | | 2000 | 54.510151908956 | | 1999 | 53.807285626792 | | 1998 | 52.478272215519 | | 1997 | 52.358387785981 | | 1996 | 51.787209768392 | | 1995 | 51.573596628801 | | 1994 | 51.090650700569 | | 1993 | 50.33865976045 | | 1992 | 49.795288423751 | | 1991 | 49.235317634667 | | 1990 | 49.479382337954 | | 1989 | 49.218571081584 | | 1988 | 48.063124298964 | | 1987 | 48.220453460785 | | 1986 | 47.708494758448 | | 1985 | 47.078677704763 | | 1984 | 46.722285908969 | | 1983 | 46.802642193459 | | 1982 | 47.522293020786 | | 1981 | 47.293786353394 | | 1980 | 46.951396870315 | | 1979 | 46.498270223712 | | 1978 | 46.026143289709 | | 1977 | 45.798835665695 | | 1976 | 45.190742752812 | | 1975 | 44.552839059973 | | 1974 | 44.527615309234 | | 1973 | 44.55784935257 | | 1972 | 43.946372385232 | | 1971 | 37.759977774679 | | 1970 | 42.30743858689 | | 1969 | 43.540718049974 | | 1968 | 43.304867823397 | | 1967 | 42.945464401025 | | 1966 | 42.390444695594 | | 1965 | 41.980495077643 | | 1964 | 41.991252241785 | | 1963 | 41.293128519828 | | 1962 | 41.168853083013 | | 1961 | 40.63054536776 | | 1960 | 40.247577602359 |
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