| Year | Value | | 2022 | 50.589099282511 | | 2021 | 50.61030008477 | | 2020 | 50.636536078508 | | 2019 | 50.672434236086 | | 2018 | 50.710039092133 | | 2017 | 50.747609312987 | | 2016 | 50.783089902513 | | 2015 | 50.82142612979 | | 2014 | 50.859594534105 | | 2013 | 50.892661495631 | | 2012 | 50.923000788948 | | 2011 | 50.950957867486 | | 2010 | 50.976466423306 | | 2009 | 50.99856906855 | | 2008 | 51.017953677528 | | 2007 | 51.035063227347 | | 2006 | 51.048698499241 | | 2005 | 51.060076383159 | | 2004 | 51.069833169204 | | 2003 | 51.079533383641 | | 2002 | 51.088747618672 | | 2001 | 51.094652329388 | | 2000 | 51.098993866437 | | 1999 | 51.102069399915 | | 1998 | 51.10529106335 | | 1997 | 51.109063708533 | | 1996 | 51.110895545285 | | 1995 | 51.110557712687 | | 1994 | 51.111490486516 | | 1993 | 51.114186769906 | | 1992 | 51.116268180709 | | 1991 | 51.119557587961 | | 1990 | 51.123162067401 | | 1989 | 51.126648733996 | | 1988 | 51.129164715247 | | 1987 | 51.130737384549 | | 1986 | 51.134826045997 | | 1985 | 51.136699696595 | | 1984 | 51.135219170313 | | 1983 | 51.136285779036 | | 1982 | 51.139145710969 | | 1981 | 51.139096378639 | | 1980 | 51.135447746085 | | 1979 | 51.130843190797 | | 1978 | 51.126425301672 | | 1977 | 51.120563256684 | | 1976 | 51.112539912623 | | 1975 | 51.104314774623 | | 1974 | 51.09693083388 | | 1973 | 51.088376004063 | | 1972 | 51.07822460712 | | 1971 | 51.069762822645 | | 1970 | 51.064606886261 | | 1969 | 51.058224997654 | | 1968 | 51.050045342035 | | 1967 | 51.043122556483 | | 1966 | 51.038129158583 | | 1965 | 51.033357426467 | | 1964 | 51.02797539417 | | 1963 | 51.022063320845 | | 1962 | 51.014692975733 | | 1961 | 51.005538656454 | | 1960 | 50.991840349977 |
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