| Year | Value | | 2022 | 48.444890651253 | | 2021 | 48.404432178263 | | 2020 | 48.413044188181 | | 2019 | 48.405989860768 | | 2018 | 48.386297896144 | | 2017 | 48.365561518015 | | 2016 | 48.347018850005 | | 2015 | 48.328178503539 | | 2014 | 48.31098251873 | | 2013 | 48.29953627978 | | 2012 | 48.290001480753 | | 2011 | 48.277532862164 | | 2010 | 48.263752131321 | | 2009 | 48.251294159481 | | 2008 | 48.241990203583 | | 2007 | 48.239047404696 | | 2006 | 48.239171930514 | | 2005 | 48.236781754107 | | 2004 | 48.233558744962 | | 2003 | 48.232886254902 | | 2002 | 48.236083479581 | | 2001 | 48.247751404787 | | 2000 | 48.247319485 | | 1999 | 48.25514713513 | | 1998 | 48.285836828099 | | 1997 | 48.314993924978 | | 1996 | 48.342598101973 | | 1995 | 48.371447807748 | | 1994 | 48.400383492466 | | 1993 | 48.426200982967 | | 1992 | 48.452037892285 | | 1991 | 48.478157707459 | | 1990 | 48.500669949157 | | 1989 | 48.518784962074 | | 1988 | 48.53587579099 | | 1987 | 48.548516489076 | | 1986 | 48.5551080839 | | 1985 | 48.560525155164 | | 1984 | 48.56484423019 | | 1983 | 48.567775505122 | | 1982 | 48.568273776473 | | 1981 | 48.569103408245 | | 1980 | 48.569533167578 | | 1979 | 48.566743744286 | | 1978 | 48.562962078428 | | 1977 | 48.557150352669 | | 1976 | 48.552823643208 | | 1975 | 48.549590671067 | | 1974 | 48.541423271066 | | 1973 | 48.533603882704 | | 1972 | 48.527331660713 | | 1971 | 48.521728274519 | | 1970 | 48.519064285023 | | 1969 | 48.514413518556 | | 1968 | 48.504000888168 | | 1967 | 48.490069953234 | | 1966 | 48.472146865695 | | 1965 | 48.447101801346 | | 1964 | 48.416507647117 | | 1963 | 48.383549010087 | | 1962 | 48.347701392329 | | 1961 | 48.308863360406 | | 1960 | 48.268094971618 |
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