| Year | Value | | 2022 | 49.527063571035 | | 2021 | 49.50658155147 | | 2020 | 49.483802481684 | | 2019 | 49.457650780878 | | 2018 | 49.430116225559 | | 2017 | 49.401442940597 | | 2016 | 49.373098932678 | | 2015 | 49.345951726157 | | 2014 | 49.317955130509 | | 2013 | 49.292473089625 | | 2012 | 49.269202158707 | | 2011 | 49.243110334422 | | 2010 | 49.214649260547 | | 2009 | 49.185681377998 | | 2008 | 49.155266582327 | | 2007 | 49.123328659211 | | 2006 | 49.092063952368 | | 2005 | 49.059570348981 | | 2004 | 49.024452293008 | | 2003 | 48.991050413102 | | 2002 | 48.96253252582 | | 2001 | 48.939138827278 | | 2000 | 48.919404794957 | | 1999 | 48.901607513336 | | 1998 | 48.884067723452 | | 1997 | 48.86843609491 | | 1996 | 48.853802796593 | | 1995 | 48.84158668479 | | 1994 | 48.827864577135 | | 1993 | 48.805407687773 | | 1992 | 48.782595394545 | | 1991 | 48.765753344374 | | 1990 | 48.755253280475 | | 1989 | 48.75156964398 | | 1988 | 48.75417262431 | | 1987 | 48.760659052062 | | 1986 | 48.788707704564 | | 1985 | 48.840837254549 | | 1984 | 48.907000875089 | | 1983 | 48.989010559612 | | 1982 | 49.080111515432 | | 1981 | 49.169657401104 | | 1980 | 49.257627168149 | | 1979 | 49.334938886037 | | 1978 | 49.397350763451 | | 1977 | 49.452824677448 | | 1976 | 49.501574358042 | | 1975 | 49.552197735922 | | 1974 | 49.611949800659 | | 1973 | 49.674635044961 | | 1972 | 49.741083672016 | | 1971 | 49.817809116477 | | 1970 | 49.882952875254 | | 1969 | 49.935562052205 | | 1968 | 49.989552791405 | | 1967 | 50.045499876935 | | 1966 | 50.104994726375 | | 1965 | 50.167696297317 | | 1964 | 50.231349291369 | | 1963 | 50.296444007487 | | 1962 | 50.365418620895 | | 1961 | 50.438748016187 | | 1960 | 50.516924560099 |
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