| Year | Value | | 2022 | 50.491277748124 | | 2021 | 50.511595392477 | | 2020 | 50.529058768256 | | 2019 | 50.544512120746 | | 2018 | 50.562791222038 | | 2017 | 50.580715912262 | | 2016 | 50.585391754934 | | 2015 | 50.576818717372 | | 2014 | 50.567865287575 | | 2013 | 50.557897130703 | | 2012 | 50.544419655451 | | 2011 | 50.532335000287 | | 2010 | 50.51629192422 | | 2009 | 50.494146368343 | | 2008 | 50.474535723593 | | 2007 | 50.449018061443 | | 2006 | 50.420450557923 | | 2005 | 50.395345315188 | | 2004 | 50.364915252057 | | 2003 | 50.330834930071 | | 2002 | 50.295586872846 | | 2001 | 50.259799665106 | | 2000 | 50.224894031013 | | 1999 | 50.188899906644 | | 1998 | 50.156679787934 | | 1997 | 50.126216923113 | | 1996 | 50.092815080967 | | 1995 | 50.060972371373 | | 1994 | 50.036753775584 | | 1993 | 50.012575194091 | | 1992 | 49.998154665259 | | 1991 | 50.00349459436 | | 1990 | 50.009247488218 | | 1989 | 50.018504346601 | | 1988 | 50.035335042462 | | 1987 | 50.084560734641 | | 1986 | 50.162196430817 | | 1985 | 50.289486874372 | | 1984 | 50.461191410982 | | 1983 | 50.596631706599 | | 1982 | 50.695613497988 | | 1981 | 50.783827624708 | | 1980 | 50.852587859768 | | 1979 | 50.921254432244 | | 1978 | 50.978393617615 | | 1977 | 51.014183394876 | | 1976 | 51.041977609012 | | 1975 | 51.072804630864 | | 1974 | 51.106460310168 | | 1973 | 51.143369440373 | | 1972 | 51.183639794368 | | 1971 | 51.227153729392 | | 1970 | 51.273308558165 | | 1969 | 51.322012915541 | | 1968 | 51.373995148218 | | 1967 | 51.429526185236 | | 1966 | 51.488196998369 | | 1965 | 51.549714813583 | | 1964 | 51.614726887267 | | 1963 | 51.684106900764 | | 1962 | 51.757628207322 | | 1961 | 51.83499921503 | | 1960 | 51.916945801816 |
|