| Year | Value | | 2022 | 1.392296984157 | | 2021 | 1.4519771111946 | | 2020 | 1.4831290153972 | | 2019 | 1.5274826691576 | | 2018 | 1.6069388001763 | | 2017 | 1.6866577462494 | | 2016 | 1.7556114034498 | | 2015 | 1.8072717280011 | | 2014 | 1.8365433221052 | | 2013 | 1.8407825771759 | | 2012 | 1.8092099068431 | | 2011 | 1.7470180503267 | | 2010 | 1.665530086186 | | 2009 | 1.5732974134484 | | 2008 | 1.4852454912372 | | 2007 | 1.4203174289779 | | 2006 | 1.3873263068887 | | 2005 | 1.359714823222 | | 2004 | 1.2695733006742 | | 2003 | 1.2692130459731 | | 2002 | 1.3686430851103 | | 2001 | 1.4333226775008 | | 2000 | 1.5006106699859 | | 1999 | 1.5575182450144 | | 1998 | 1.5428058618971 | | 1997 | 1.4444728296611 | | 1996 | 1.746584738891 | | 1995 | 2.239084123293 | | 1994 | 2.4824860654177 | | 1993 | 2.6472546939948 | | 1992 | 2.6998274238818 | | 1991 | 2.6918409315831 | | 1990 | 2.6964490851126 | | 1989 | 2.6922264373386 | | 1988 | 2.7205326799642 | | 1987 | 2.7702142368353 | | 1986 | 2.7307481123079 | | 1985 | 2.6439771571004 | | 1984 | 2.5612642982938 | | 1983 | 2.5043300022613 | | 1982 | 2.4597689398456 | | 1981 | 2.4167142187882 | | 1980 | 2.4221593359344 | | 1979 | 2.4659269578138 | | 1978 | 2.4998024280864 | | 1977 | 2.5419460431651 | | 1976 | 2.5995789809239 | | 1975 | 2.6655085489422 | | 1974 | 2.7204145214522 | | 1973 | 2.7512606947101 | | 1972 | 2.7845331804197 | | 1971 | 2.821678037692 | | 1970 | 2.8509259447165 | | 1969 | 2.8913348895991 | | 1968 | 2.9566634538556 | | 1967 | 3.0421547591202 | | 1966 | 3.1373498461643 | | 1965 | 3.2396298467427 | | 1964 | 3.3345944066305 | | 1963 | 3.407982555346 | | 1962 | 3.4546518285527 | | 1961 | 3.4669874853372 |
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