| Year | Value | | 2021 | 1.5955788974224 | | 2020 | 1.5955788974224 | | 2019 | 1.5955788974224 | | 2018 | 1.5955788974224 | | 2017 | 1.5993003642386 | | 2016 | 1.6174425149673 | | 2015 | 1.6234898985435 | | 2014 | 1.5955788974224 | | 2013 | 1.4271825239918 | | 2012 | 1.4499765082407 | | 2011 | 1.4695142090255 | | 2010 | 1.4792830594179 | | 2009 | 1.4867259930502 | | 2008 | 1.5532472123888 | | 2007 | 1.6030218310547 | | 2006 | 1.6048825644628 | | 2005 | 1.6281417320637 | | 2004 | 1.6281417320637 | | 2003 | 1.6746600672655 | | 2002 | 1.6746600672655 | | 2001 | 1.6746600672655 | | 2000 | 1.6709386004494 | | 1999 | 1.6718689671534 | | 1998 | 1.6918718512902 | | 1997 | 1.6928022179942 | | 1996 | 1.6960585014584 | | 1995 | 1.7002451516265 | | 1994 | 1.7058273518507 | | 1993 | 1.7081532686108 | | 1992 | 1.6979192348664 | | 1991 | 1.6648912168731 | | 1990 | 1.5769715633417 | | 1989 | 1.4885867264582 | | 1988 | 1.4188092236555 | | 1987 | 1.3490317208528 | | 1986 | 1.2559950504491 | | 1985 | 1.1862175476464 | | 1984 | 1.0931808772428 | | 1983 | 1.02340337444 | | 1982 | 0.92571487051621 | | 1981 | 0.9024557029153 | | 1980 | 0.87919653531439 | | 1979 | 0.85593736771348 | | 1978 | 0.83267820011257 | | 1977 | 0.80941903251166 | | 1976 | 0.78150803139057 | | 1975 | 0.75359703026948 | | 1974 | 0.72568602914839 | | 1973 | 0.6977750280273 | | 1972 | 0.67451586042639 | | 1971 | 0.65125669282548 | | 1970 | 0.63264935874475 | | 1969 | 0.61404202466402 | | 1968 | 0.60008652410347 | | 1967 | 0.58613102354293 | | 1966 | 0.57682735650257 | | 1965 | 0.5675236894622 | | 1964 | 0.55822002242184 | | 1963 | 0.54891635538147 | | 1962 | 0.53961268834111 | | 1961 | 0.53030902130075 |
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