| Year | Value | | 2022 | 49.386245788543 | | 2021 | 49.362140726474 | | 2020 | 49.339824627895 | | 2019 | 49.31571711537 | | 2018 | 49.288996366149 | | 2017 | 49.261314611033 | | 2016 | 49.232074097654 | | 2015 | 49.202395413096 | | 2014 | 49.17097313213 | | 2013 | 49.138302214751 | | 2012 | 49.105321721747 | | 2011 | 49.072073197486 | | 2010 | 49.04046655862 | | 2009 | 49.009164508027 | | 2008 | 48.976405355707 | | 2007 | 48.941245246703 | | 2006 | 48.906258508116 | | 2005 | 48.873715040737 | | 2004 | 48.842435351211 | | 2003 | 48.812642847316 | | 2002 | 48.785932402981 | | 2001 | 48.763142407228 | | 2000 | 48.742778358678 | | 1999 | 48.73739508684 | | 1998 | 48.752988629905 | | 1997 | 48.755164769369 | | 1996 | 48.736283583084 | | 1995 | 48.718786418456 | | 1994 | 48.703351728176 | | 1993 | 48.689628023744 | | 1992 | 48.679641491284 | | 1991 | 48.674757711379 | | 1990 | 48.673567178299 | | 1989 | 48.67376510453 | | 1988 | 48.674873817704 | | 1987 | 48.678705913779 | | 1986 | 48.686608570847 | | 1985 | 48.697127391988 | | 1984 | 48.709786619424 | | 1983 | 48.72523194795 | | 1982 | 48.743696353493 | | 1981 | 48.766860325437 | | 1980 | 48.794051922998 | | 1979 | 48.749996957149 | | 1978 | 48.707712682922 | | 1977 | 48.745760714075 | | 1976 | 48.789899231972 | | 1975 | 48.840798320283 | | 1974 | 48.903742286425 | | 1973 | 48.984172824074 | | 1972 | 49.073579998322 | | 1971 | 49.176199871825 | | 1970 | 49.280080045566 | | 1969 | 49.385418792951 | | 1968 | 49.493637259523 | | 1967 | 49.600962712337 | | 1966 | 49.720096427789 | | 1965 | 49.85146406573 | | 1964 | 49.990600883009 | | 1963 | 50.132762226377 | | 1962 | 50.229082366332 | | 1961 | 50.277221847791 | | 1960 | 50.255479441389 |
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