| Year | Value | | 2022 | 0.64988678893937 | | 2021 | 0.31363072926603 | | 2020 | 1.5755227123029 | | 2019 | 1.7923037576399 | | 2018 | 0.15085389256922 | | 2017 | 2.2333321991708 | | 2016 | 0.45404601428247 | | 2015 | 0.94137596886662 | | 2014 | 1.1618168099914 | | 2013 | 1.6695517828041 | | 2012 | 1.3414717323305 | | 2011 | 1.1304053407843 | | 2010 | 1.0134886278493 | | 2009 | 1.2310704154081 | | 2008 | 1.7935528517957 | | 2007 | 1.8889931062003 | | 2006 | 1.9784922172232 | | 2005 | 1.8317137492463 | | 2004 | 1.2883018123651 | | 2003 | 1.1826906272114 | | 2002 | 1.1533735955117 | | 2001 | 1.5551079111326 | | 2000 | 1.5265701288491 | | 1999 | 1.4371990037847 | | 1998 | 1.5885552045427 | | 1997 | 1.7952850521658 | | 1996 | 1.0394833835524 | | 1995 | 1.5490621597726 | | 1994 | 1.5907469248441 | | 1993 | 2.1452538550395 | | 1992 | 1.6434788501941 | | 1991 | 1.840335276824 | | 1990 | 1.5180365557242 | | 1989 | 2.7935969411796 | | 1988 | 1.8161050828098 | | 1987 | 1.6336983398092 | | 1986 | 1.6499705362404 | | 1985 | 1.3696189564172 | | 1984 | 2.2920517560074 | | 1983 | 2.9707401032702 | | 1982 | 2.2487726164727 | | 1981 | 1.5216857753936 | | 1980 | 1.6955153422502 | | 1979 | 1.9158563589102 | | 1978 | 2.1057612681888 | | 1977 | 2.0679468242245 | | 1976 | 1.8874907475944 | | 1975 | 2.5910245554615 | | 1974 | 2.307760848258 | | 1973 | 2.4709897610922 | | 1972 | 2.8292682926829 | | 1971 | 2.6994078718217 | | 1970 | 2.2940164404512 | | 1969 | 2.4989228780698 | | 1968 | 2.6773761713521 | | 1967 | 2.8585154936344 | | 1966 | 2.6568825910931 | | 1965 | 2.6364355391511 | | 1964 | 2.4466891133558 | | 1963 | 2.5535880708294 | | 1962 | 2.3129021334236 | | 1961 | 1.4222222222222 | | 1960 | 3.0580444098169 |
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