| Year | Value | | 2022 | 39.132154418266 | | 2021 | 38.90530433665 | | 2020 | 37.914653764726 | | 2019 | 36.457779318879 | | 2018 | 35.421286428609 | | 2017 | 34.808208277941 | | 2016 | 34.8274129334 | | 2015 | 35.244607536281 | | 2014 | 35.365417169772 | | 2013 | 35.557552637371 | | 2012 | 36.639515055384 | | 2011 | 38.458216266952 | | 2010 | 40.702533108205 | | 2009 | 42.128652915604 | | 2008 | 42.332144360603 | | 2007 | 42.546570979008 | | 2006 | 42.770680401726 | | 2005 | 43.003993333312 | | 2004 | 43.246687229505 | | 2003 | 43.286519164336 | | 2002 | 43.099457951398 | | 2001 | 42.892666844377 | | 2000 | 42.678243346601 | | 1999 | 42.456023523307 | | 1998 | 42.22567000347 | | 1997 | 41.987176632579 | | 1996 | 41.739797769912 | | 1995 | 41.481318855308 | | 1994 | 41.20941567952 | | 1993 | 41.301810733116 | | 1992 | 41.829674893602 | | 1991 | 42.438767256213 | | 1990 | 43.108431918888 | | 1989 | 43.850410598901 | | 1988 | 44.677113253211 | | 1987 | 45.602605013464 | | 1986 | 46.642964128897 | | 1985 | 47.820310369773 | | 1984 | 48.528633337155 | | 1983 | 48.660663143582 | | 1982 | 48.811518218819 | | 1981 | 48.973061218418 | | 1980 | 49.135790820689 | | 1979 | 49.306119991571 | | 1978 | 49.49164612435 | | 1977 | 49.679953447774 | | 1976 | 49.853594488891 | | 1975 | 49.989837320915 | | 1974 | 50.044124895982 | | 1973 | 50.039047649112 | | 1972 | 50.029447280893 | | 1971 | 50.022720574678 | | 1970 | 50.019755685537 | | 1969 | 50.014152538353 | | 1968 | 50.006511039742 | | 1967 | 49.996624022172 | | 1966 | 49.984033920512 | | 1965 | 49.967497911783 | | 1964 | 49.948177072573 | | 1963 | 49.924112254068 | | 1962 | 49.895089017283 | | 1961 | 49.861010206005 | | 1960 | 49.820614179774 |
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