| Year | Value | | 2022 | 0.43364720204809 | | 2021 | 0.25486190314841 | | 2020 | 0.059005754772927 | | 2019 | 0.025810733721203 | | 2018 | 0.1328462500256 | | 2017 | 0.21810259463602 | | 2016 | 0.28164857041114 | | 2015 | 0.52464260541548 | | 2014 | 1.6551064297068 | | 2013 | 1.7794404276941 | | 2012 | 1.8116790430764 | | 2011 | 1.8250853740111 | | 2010 | 1.5332154287314 | | 2009 | 1.3096156069914 | | 2008 | 1.4523076838371 | | 2007 | 1.4737108819497 | | 2006 | 1.4957543819619 | | 2005 | 1.5184673538317 | | 2004 | 1.5214610980675 | | 2003 | 1.7037651435772 | | 2002 | 1.898811418807 | | 2001 | 1.9017932212971 | | 2000 | 1.9013743780407 | | 1999 | 1.8987622097442 | | 1998 | 1.8987678790139 | | 1997 | 1.9319768189133 | | 1996 | 1.9153327092665 | | 1995 | 2.2615222184796 | | 1994 | 2.66662501748 | | 1993 | 2.5788222741968 | | 1992 | 2.498715148269 | | 1991 | 2.5779670074749 | | 1990 | 2.368989135685 | | 1989 | 1.9652846425313 | | 1988 | 1.9436058377119 | | 1987 | 1.9821319059655 | | 1986 | 1.8602204145825 | | 1985 | 1.829518523 | | 1984 | 1.9644380668481 | | 1983 | 2.038114026495 | | 1982 | 2.115563554165 | | 1981 | 1.8394575953391 | | 1980 | 1.1129176078725 | | 1979 | 0.72464085207673 | | 1978 | 1.0969031370574 | | 1977 | 1.4815085785141 | | 1976 | 1.1257154524635 | | 1975 | 1.1385322225125 | | 1974 | 1.9268418865877 | | 1973 | 2.3623145763436 | | 1972 | 4.4814015789793 | | 1971 | 6.8992871486951 | | 1970 | 7.4107972153722 | | 1969 | 4.4233254976826 | | 1968 | 3.0614635819607 | | 1967 | 3.1581572050299 | | 1966 | 3.2611585588761 | | 1965 | 2.6877317763747 | | 1964 | 2.76197073384 | | 1963 | 2.7204516239033 | | 1962 | 2.6733062197069 | | 1961 | 2.7467394700611 |
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