| Year | Value | | 2022 | 8.5468699318845 | | 2021 | 2.7666666666667 | | 2020 | 1.3819106335186 | | 2019 | 1.5308956415264 | | 2018 | 1.9983798142954 | | 2017 | 2.0812691138559 | | 2016 | 0.89159175265536 | | 2015 | 0.89656333526032 | | 2014 | 1.6058118295447 | | 2013 | 2.000156169006 | | 2012 | 2.4856756217702 | | 2011 | 3.2865791487538 | | 2010 | 1.8135343899506 | | 2009 | 0.50630882769651 | | 2008 | 3.2159503323989 | | 2007 | 2.1685552880075 | | 2006 | 1.4415485111902 | | 2005 | 2.2991378563928 | | 2004 | 2.0612061803286 | | 2003 | 1.3555537089645 | | 2002 | 1.8103578776413 | | 2001 | 2.6500007727953 | | 2000 | 2.3448628535728 | | 1999 | 0.56899376588557 | | 1998 | 0.9224671966808 | | 1997 | 1.3059785722769 | | 1996 | 1.8609711576043 | | 1995 | 2.243366315009 | | 1994 | 2.9534093676108 | | 1993 | 3.6317852494318 | | 1992 | 4.0208478003856 | | 1991 | 3.3374270347479 | | 1990 | 3.2618723187858 | | 1989 | 2.5683482902937 | | 1988 | 1.9157168467126 | | 1987 | 1.4019527178397 | | 1986 | 1.7054445673197 | | 1985 | 3.1895168180519 | | 1984 | 5.6631857390935 | | 1983 | 3.3391645340953 | | 1982 | 5.4360308251285 | | 1981 | 6.8030417759926 | | 1980 | 6.328325362261 | | 1979 | 3.7074009635341 | | 1978 | 3.5743185755122 | | 1977 | 5.4946156812767 | | 1976 | 7.3186854510692 | | 1975 | 8.4452586391797 | | 1974 | 9.5217881974224 | | 1973 | 7.5310780382712 | | 1972 | 6.3551461268679 | | 1971 | 4.704258138287 | | 1970 | 4.3728244158214 | | 1969 | 3.0804041953953 | | 1968 | 2.7648644733977 | | 1967 | 3.9746729289883 | | 1966 | 2.0548205925799 | | 1965 | 4.9309163767627 | | 1964 | 3.8685635493663 | | 1963 | 2.7087669949983 | | 1962 | 4.3817986385118 | | 1961 | 3.5422398672756 | | 1960 | 1.9457493519864 |
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