| Year | Value | | 2022 | 0.69078154796542 | | 2021 | 0.41375102447215 | | 2020 | 0.21506783712958 | | 2019 | 0.045255710110623 | | 2018 | 0.12678695165284 | | 2017 | 0.26586093225552 | | 2016 | 0.29511060484548 | | 2015 | 0.23785500198466 | | 2014 | 0.26937876716512 | | 2013 | 0.27536875707442 | | 2012 | 0.51643760654804 | | 2011 | 0.28336043594695 | | 2010 | 0.2260138756897 | | 2009 | 0.15490881395062 | | 2008 | 0.17509736747488 | | 2007 | 0.15491515806095 | | 2006 | 0.15571648465158 | | 2005 | 0.1988788432371 | | 2004 | 0.22143937865481 | | 2003 | 0.28643326812869 | | 2002 | 0.28475137719698 | | 2001 | 0.22937918330845 | | 2000 | 0.25976490828863 | | 1999 | 0.28326061048519 | | 1998 | 0.2326793368665 | | 1997 | 0.20145893633581 | | 1996 | 0.17177160862902 | | 1995 | 0.13922000360143 | | 1994 | 0.13688310430324 | | 1993 | 0.11403559439276 | | 1992 | 0.039136583268413 | | 1991 | 0.0056681833892284 | | 1990 | -1.0331172969002 | | 1989 | -1.088983893402 | | 1988 | 0.15327293555496 | | 1987 | 0.16779878820112 | | 1986 | 0.17057914515342 | | 1985 | 0.18184716343174 | | 1984 | 0.20009784947921 | | 1983 | 0.15024075275147 | | 1982 | 0.058952115511336 | | 1981 | 0.0067777717121334 | | 1980 | 0.065093729327113 | | 1979 | 0.18074738192239 | | 1978 | 0.3449237331353 | | 1977 | 0.46458104257405 | | 1976 | 0.55018298882792 | | 1975 | 0.58808180904707 | | 1974 | 0.44632566192729 | | 1973 | 0.32227702792653 | | 1972 | 0.29810251534184 | | 1971 | 0.28617609868192 | | 1970 | 0.37978140233221 | | 1969 | 0.41750451727434 | | 1968 | 0.3830621867148 | | 1967 | 0.37215558305245 | | 1966 | 0.30224475828958 | | 1965 | 0.27728771349504 | | 1964 | 0.31560144966103 | | 1963 | 0.26018292584822 | | 1962 | 0.32266128504507 | | 1961 | 0.45323964398849 |
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