| Year | Value | | 2022 | 3.378698625499 | | 2021 | 2.4771024146545 | | 2020 | -1.1387021539303 | | 2019 | 0.66289186576441 | | 2018 | 0.88470916057099 | | 2017 | 3.871201157742 | | 2016 | 2.0905665952581 | | 2015 | 2.1043898023835 | | 2014 | 3.1429905087904 | | 2013 | 2.1050123123368 | | 2012 | 1.6635710247914 | | 2011 | 3.1744709215131 | | 2010 | 1.6228523557707 | | 2009 | 0.5833084056237 | | 2008 | 5.4407822110077 | | 2007 | 2.0273531777957 | | 2006 | 3.6092356422439 | | 2005 | 2.9750709268445 | | 2004 | 1.421271159374 | | 2003 | 1.0896763257729 | | 2002 | 1.8078724628153 | | 2001 | 1.4167847320611 | | 2000 | 1.534740236977 | | 1999 | 2.744561302406 | | 1998 | 5.2703420034877 | | 1997 | 2.6625145971195 | | 1996 | 3.4885594585892 | | 1995 | 3.450575095849 | | 1994 | 3.7249705535928 | | 1993 | 3.5365853658539 | | 1992 | 4.7672282999282 | | 1991 | 4.358333333333 | | 1990 | 2.6178010471205 | | 1989 | 2.813200897148 | | 1988 | 2.5565194532074 | | 1987 | 0.29000790943841 | | 1986 | 0.73700285539194 | | 1985 | 0.34645879125987 | | 1984 | 3.8972726014977 | | 1983 | 3.7042354631937 | | 1982 | 5.8189000297783 | | 1981 | 9.7000000000002 | | 1980 | 6.6749195345051 | | 1979 | 3.6544679979641 | | 1978 | 4.8600645855425 | | 1977 | 4.7882240144597 | | 1976 | 2.6337115073057 | | 1975 | 4.487722269159 | | 1974 | 17.328980982441 | | 1973 | 10.56017574131 | | 1972 | 3.2315542235488 | | 1971 | 1.613035963958 | | 1970 | 1.8439359655639 | | 1969 | 0.40901502529407 | | 1968 | 0.15834652879457 | | 1967 | 4.5755621403329 | | 1966 | 0.96796902526133 | | 1965 | 0.10548523224379 | | 1964 | 0.40273157100361 | | 1963 | 3.1052536560835 | | 1962 | 0.10844026784809 | | 1961 | 0.18040772163161 | | 1960 | 0.063182597888167 |
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