| Year | Value | | 2022 | 0.44582965495802 | | 2021 | 1.3551773915221 | | 2020 | 1.9491345715378 | | 2019 | 2.9672305396414 | | 2018 | 3.5996403479479 | | 2017 | 3.9262877948038 | | 2016 | 4.1969042237483 | | 2015 | 4.4225340915776 | | 2014 | 3.9174834060424 | | 2013 | 3.3466404024458 | | 2012 | 3.4384912386764 | | 2011 | 3.4962087543748 | | 2010 | 3.5291555184817 | | 2009 | 3.5442244712798 | | 2008 | 3.5522889557995 | | 2007 | 3.3543558292615 | | 2006 | 2.3762863421333 | | 2005 | 1.6032440431433 | | 2004 | 1.6381145165317 | | 2003 | 1.6766859857067 | | 2002 | 1.7115433467015 | | 2001 | 1.6907169828835 | | 2000 | 1.5683014465669 | | 1999 | 1.5637011031065 | | 1998 | 1.752323611182 | | 1997 | 1.9513418452044 | | 1996 | 2.1581187313874 | | 1995 | 2.353907303608 | | 1994 | 2.552513258311 | | 1993 | 2.7668828299027 | | 1992 | 2.9648713281949 | | 1991 | 3.1474441636677 | | 1990 | 3.1703242631748 | | 1989 | 3.158989024209 | | 1988 | 3.3242030881769 | | 1987 | 3.5028900092493 | | 1986 | 3.5307376324381 | | 1985 | 3.1995599573718 | | 1984 | 2.7764363575591 | | 1983 | 2.7221331392925 | | 1982 | 2.8242421467611 | | 1981 | 2.8553725847042 | | 1980 | 2.8051148453988 | | 1979 | 2.719299152579 | | 1978 | 2.7505088169586 | | 1977 | 2.8899959560061 | | 1976 | 2.9885841906801 | | 1975 | 2.9654386927833 | | 1974 | 2.9240739056547 | | 1973 | 2.9709250789722 | | 1972 | 3.04143479011 | | 1971 | 3.0548620330408 | | 1970 | 3.0264405583365 | | 1969 | 2.9881094886806 | | 1968 | 3.0641603530463 | | 1967 | 3.4659529984998 | | 1966 | 3.8892931202229 | | 1965 | 3.231463784328 | | 1964 | 2.4659276849454 | | 1963 | 2.5043977779367 | | 1962 | 2.5016544966092 | | 1961 | 2.4807039266282 |
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