| Year | Value | | 2022 | 50.12402146187 | | 2021 | 50.111381534421 | | 2020 | 50.09490443238 | | 2019 | 50.082246422397 | | 2018 | 50.078071769248 | | 2017 | 50.074025649407 | | 2016 | 50.072813636186 | | 2015 | 50.075078061295 | | 2014 | 50.07822903639 | | 2013 | 50.082319606517 | | 2012 | 50.088982961606 | | 2011 | 50.104276407731 | | 2010 | 50.116395260736 | | 2009 | 50.114524386958 | | 2008 | 50.116089285304 | | 2007 | 50.118637581324 | | 2006 | 50.117966510786 | | 2005 | 50.118134586838 | | 2004 | 50.121435410946 | | 2003 | 50.130071148919 | | 2002 | 50.143151740845 | | 2001 | 50.155205185357 | | 2000 | 50.164910864634 | | 1999 | 50.179820602505 | | 1998 | 50.197439015666 | | 1997 | 50.215028767362 | | 1996 | 50.235577349127 | | 1995 | 50.254364014818 | | 1994 | 50.270154439563 | | 1993 | 50.286311650622 | | 1992 | 50.299248694766 | | 1991 | 50.307107341328 | | 1990 | 50.282941259566 | | 1989 | 50.232874962748 | | 1988 | 50.195174347017 | | 1987 | 50.163067825464 | | 1986 | 50.126645008535 | | 1985 | 50.074572964252 | | 1984 | 49.988037934103 | | 1983 | 49.876278616659 | | 1982 | 49.759736849927 | | 1981 | 49.60270243017 | | 1980 | 49.432157185475 | | 1979 | 49.309071008346 | | 1978 | 49.221338456059 | | 1977 | 49.146723662499 | | 1976 | 49.059924158133 | | 1975 | 48.959168729732 | | 1974 | 48.835358538526 | | 1973 | 48.680764380638 | | 1972 | 48.512401806148 | | 1971 | 48.349026834625 | | 1970 | 48.172924480879 | | 1969 | 47.893083001354 | | 1968 | 47.50933247702 | | 1967 | 47.103202653472 | | 1966 | 46.667217881406 | | 1965 | 46.203819880106 | | 1964 | 45.713601532567 | | 1963 | 45.18158014572 | | 1962 | 44.598676639816 | | 1961 | 43.972054435631 | | 1960 | 43.685881419207 |
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