| Year | Value | | 2022 | 2.0820872224982 | | 2021 | 2.0588607802276 | | 2020 | 2.0311686033774 | | 2019 | 1.9423619801398 | | 2018 | 1.9153959369473 | | 2017 | 1.9054894406825 | | 2016 | 2.012596656876 | | 2015 | 2.0354136375277 | | 2014 | 2.0585945375369 | | 2013 | 2.1823544887698 | | 2012 | 3.5382980554915 | | 2011 | 3.931537101803 | | 2010 | 2.8996272740125 | | 2009 | 3.1522896392818 | | 2008 | 4.0764603685106 | | 2007 | 5.0049827927467 | | 2006 | 5.6273999933896 | | 2005 | 4.5046367323306 | | 2004 | 1.2009255713843 | | 2003 | 0.79970851394113 | | 2002 | 2.6134480649165 | | 2001 | 2.9413684976466 | | 2000 | 3.711300592068 | | 1999 | 5.546454233948 | | 1998 | 10.199885262962 | | 1997 | 7.8227617251615 | | 1996 | 2.8321499914998 | | 1995 | 0.80719902530922 | | 1994 | 0.35570986942671 | | 1993 | 3.8302124189783 | | 1992 | 5.6825867933816 | | 1991 | -13.057670758726 | | 1990 | -12.645533175344 | | 1989 | 2.747604287804 | | 1988 | 2.7927322580647 | | 1987 | 2.8469046143326 | | 1986 | 2.9101064825933 | | 1985 | 2.9694622841503 | | 1984 | 3.0372524300895 | | 1983 | 2.9616144493246 | | 1982 | 2.869050464695 | | 1981 | 2.9335641622365 | | 1980 | 2.9732725548306 | | 1979 | 2.9601014390293 | | 1978 | 2.9408467085462 | | 1977 | 2.8459656058615 | | 1976 | 2.7640948257978 | | 1975 | 2.7503352022409 | | 1974 | 2.7166688861446 | | 1973 | 2.6702042173883 | | 1972 | 2.5858480675994 | | 1971 | 2.5695957298204 | | 1970 | 2.6085408055199 | | 1969 | 2.5878321145594 | | 1968 | 2.5635027933136 | | 1967 | 2.5404772085467 | | 1966 | 2.5311690581721 | | 1965 | 2.5266121534598 | | 1964 | 2.5030285921956 | | 1963 | 2.4882044738207 | | 1962 | 2.4654822862358 | | 1961 | 2.4309297152628 |
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