| Year | Value | | 2022 | 48.450827014422 | | 2021 | 48.43450292739 | | 2020 | 48.414242162489 | | 2019 | 48.394080169548 | | 2018 | 48.374633284331 | | 2017 | 48.350563964701 | | 2016 | 48.325456402108 | | 2015 | 48.302054356125 | | 2014 | 48.282552919483 | | 2013 | 48.266818093092 | | 2012 | 48.253391367235 | | 2011 | 48.241823849511 | | 2010 | 48.232011026498 | | 2009 | 48.223767073067 | | 2008 | 48.216943844447 | | 2007 | 48.212534146716 | | 2006 | 48.211831506176 | | 2005 | 48.215235715481 | | 2004 | 48.240525004368 | | 2003 | 48.289651205576 | | 2002 | 48.343732732567 | | 2001 | 48.397440849407 | | 2000 | 48.445701143057 | | 1999 | 48.485695020041 | | 1998 | 48.520956525657 | | 1997 | 48.555577708825 | | 1996 | 48.589721855569 | | 1995 | 48.624349343889 | | 1994 | 48.659240206336 | | 1993 | 48.693921677864 | | 1992 | 48.728807647574 | | 1991 | 48.763560583203 | | 1990 | 48.798593011512 | | 1989 | 48.833641231174 | | 1988 | 48.868430286962 | | 1987 | 48.904385954302 | | 1986 | 48.942540867847 | | 1985 | 48.975966679651 | | 1984 | 49.003691508865 | | 1983 | 49.031782807183 | | 1982 | 49.060748890132 | | 1981 | 49.091897847527 | | 1980 | 49.124976724503 | | 1979 | 49.158116915908 | | 1978 | 49.191548410029 | | 1977 | 49.226986172403 | | 1976 | 49.265018709181 | | 1975 | 49.320826602998 | | 1974 | 49.393605523993 | | 1973 | 49.466533889119 | | 1972 | 49.538971871116 | | 1971 | 49.605915825103 | | 1970 | 49.667325504925 | | 1969 | 49.726545869312 | | 1968 | 49.778991343722 | | 1967 | 49.82453263305 | | 1966 | 49.867086807313 | | 1965 | 49.907682619225 | | 1964 | 49.947028626409 | | 1963 | 49.982386150482 | | 1962 | 50.015178744666 | | 1961 | 50.049723698662 | | 1960 | 50.086140051822 |
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