| Year | Value | | 2022 | 2.5344983166673 | | 2021 | 2.8513576544993 | | 2020 | 3.1347469077916 | | 2019 | 2.9085290926874 | | 2018 | 2.8852079730485 | | 2017 | 2.8664921475007 | | 2016 | 2.5815493989566 | | 2015 | 3.1213412289087 | | 2014 | 3.6575760653036 | | 2013 | 3.4667883041098 | | 2012 | 4.0776277285879 | | 2011 | 3.6895083023074 | | 2010 | 2.8949041037099 | | 2009 | 3.5612883744667 | | 2008 | 2.0023332623226 | | 2007 | 1.7931957274721 | | 2006 | 4.1396780353435 | | 2005 | 3.5765080035446 | | 2004 | 3.9331776884731 | | 2003 | 7.5410189648018 | | 2002 | 6.449321477973 | | 2001 | 0.74251683439631 | | 2000 | 1.4438030241194 | | 1999 | 4.077879484722 | | 1998 | 3.8829306048975 | | 1997 | 3.9106052193522 | | 1996 | 4.1030220499493 | | 1995 | 6.0465355523399 | | 1994 | 9.8642620662834 | | 1993 | 14.964454874687 | | 1992 | 11.52252441518 | | 1991 | 0.46988040676563 | | 1990 | 0.20243395567188 | | 1989 | 2.7518772934069 | | 1988 | 0.58631831168329 | | 1987 | -1.2101903975545 | | 1986 | 0.60856087267726 | | 1985 | 2.5876969334881 | | 1984 | 2.894334707001 | | 1983 | -1.3657077442312 | | 1982 | -10.053006253118 | | 1981 | -11.275324328166 | | 1980 | -3.9241716935363 | | 1979 | 0.36649280521328 | | 1978 | 1.9633768896909 | | 1977 | 2.0869511264525 | | 1976 | 2.1795174361392 | | 1975 | 2.3932871520194 | | 1974 | 2.513006528667 | | 1973 | 2.5244212365997 | | 1972 | 2.4293956927432 | | 1971 | 2.4153691740762 | | 1970 | 2.4331826248067 | | 1969 | 2.378916547433 | | 1968 | 2.3473506434931 | | 1967 | 2.2926378897609 | | 1966 | 2.2535240122801 | | 1965 | 2.2160069208253 | | 1964 | 2.1396508437265 | | 1963 | 2.0789966265522 | | 1962 | 2.0148788633946 | | 1961 | 1.9259516111087 |
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