| Year | Value | | 2022 | 1.6283392541792 | | 2021 | 1.6577032008427 | | 2020 | 1.7324567280315 | | 2019 | 1.8394448856862 | | 2018 | 1.9033254281097 | | 2017 | 1.9570024707508 | | 2016 | 1.9934316887991 | | 2015 | 1.9999460506958 | | 2014 | 1.9790488103591 | | 2013 | 1.9667158178046 | | 2012 | 1.9431021343597 | | 2011 | 1.8983942809434 | | 2010 | 1.8587019905244 | | 2009 | 1.7959039315283 | | 2008 | 1.7089716747672 | | 2007 | 1.6279086770294 | | 2006 | 1.4411372964252 | | 2005 | 1.3640819625121 | | 2004 | 1.4072732151523 | | 2003 | 1.3542389111181 | | 2002 | 1.3488669523342 | | 2001 | 1.3759308026136 | | 2000 | 1.4022908582876 | | 1999 | 1.3984291241086 | | 1998 | 1.510573237254 | | 1997 | 1.6811597116284 | | 1996 | 1.7633195606331 | | 1995 | 1.9180441993833 | | 1994 | 2.1077465126965 | | 1993 | 2.2403692686541 | | 1992 | 2.3237518628326 | | 1991 | 2.3846528039865 | | 1990 | 2.4940676377263 | | 1989 | 2.6317650630359 | | 1988 | 2.7471060541595 | | 1987 | 3.0282855405313 | | 1986 | 3.3309327237223 | | 1985 | 3.397687535105 | | 1984 | 3.3819416132164 | | 1983 | 3.3532050191695 | | 1982 | 3.2974527326651 | | 1981 | 3.2135460991597 | | 1980 | 3.1021369620531 | | 1979 | 2.9853702086293 | | 1978 | 2.8676014248673 | | 1977 | 3.76843461239 | | 1976 | 4.8159437395612 | | 1975 | 3.6993956277684 | | 1974 | 2.4525753645833 | | 1973 | 2.3727824036842 | | 1972 | 2.3081709871858 | | 1971 | 2.2530438067529 | | 1970 | 2.2348551417655 | | 1969 | 2.2491098798423 | | 1968 | 2.2529240688533 | | 1967 | 2.2244774119789 | | 1966 | 1.8575152756726 | | 1965 | 1.6462430250204 | | 1964 | 1.7363631961726 | | 1963 | 1.6102194522496 | | 1962 | 1.5370368422173 | | 1961 | 1.7771246210905 |
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