| Year | Value | | 2022 | 49.098267236729 | | 2021 | 49.105165445392 | | 2020 | 49.107297668406 | | 2019 | 49.10202868821 | | 2018 | 49.089241509673 | | 2017 | 49.070346779855 | | 2016 | 49.048194514762 | | 2015 | 49.019168281211 | | 2014 | 48.987559715789 | | 2013 | 48.958940897552 | | 2012 | 48.931311535081 | | 2011 | 48.907396814602 | | 2010 | 48.884582041492 | | 2009 | 48.863011940152 | | 2008 | 48.844308627113 | | 2007 | 48.824329535998 | | 2006 | 48.806135566828 | | 2005 | 48.791206971386 | | 2004 | 48.774002149097 | | 2003 | 48.75892921141 | | 2002 | 48.747801961588 | | 2001 | 48.732817231309 | | 2000 | 48.712124497131 | | 1999 | 48.688672533686 | | 1998 | 48.663378521424 | | 1997 | 48.635421428309 | | 1996 | 48.604086285796 | | 1995 | 48.565829848039 | | 1994 | 48.518559798892 | | 1993 | 48.449507757175 | | 1992 | 48.367079439979 | | 1991 | 48.290924742611 | | 1990 | 48.209903033949 | | 1989 | 48.182585786301 | | 1988 | 48.287156888972 | | 1987 | 48.461106297801 | | 1986 | 48.630088427053 | | 1985 | 48.791001492797 | | 1984 | 48.93896540278 | | 1983 | 48.990826483344 | | 1982 | 48.948791174287 | | 1981 | 48.906376220181 | | 1980 | 48.869110364653 | | 1979 | 48.831052660368 | | 1978 | 48.790669125619 | | 1977 | 48.750010412152 | | 1976 | 48.7085457317 | | 1975 | 48.669230883909 | | 1974 | 48.636016033711 | | 1973 | 48.605840717569 | | 1972 | 48.574090659762 | | 1971 | 48.54012908932 | | 1970 | 48.505495321551 | | 1969 | 48.469662019175 | | 1968 | 48.430269806011 | | 1967 | 48.38847952987 | | 1966 | 48.348044162892 | | 1965 | 48.306857650009 | | 1964 | 48.262108149619 | | 1963 | 48.217766343332 | | 1962 | 48.173666927577 | | 1961 | 48.12905986825 | | 1960 | 48.088363342702 |
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