| Year | Value | | 2022 | 13.895660977518 | | 2021 | 5.2140494051304 | | 2020 | 5.0449328897754 | | 2019 | 9.152799593248 | | 2018 | 14.401465780742 | | 2017 | 29.506608394004 | | 2016 | 13.813606214829 | | 2015 | 10.370490343517 | | 2014 | 10.070215468748 | | 2013 | 9.4697198106492 | | 2012 | 7.1117294334308 | | 2011 | 10.064925987482 | | 2010 | 11.265188265319 | | 2009 | 11.763495438644 | | 2008 | 18.316831683168 | | 2007 | 9.3189690579923 | | 2006 | 7.6445264452643 | | 2005 | 4.8693969687199 | | 2004 | 11.270619332052 | | 2003 | 4.507776363193 | | 2002 | 2.7372385500033 | | 2001 | 2.2697572047596 | | 2000 | 2.6838053534855 | | 1999 | 3.0794991263833 | | 1998 | 3.8725754642749 | | 1997 | 4.6256057882644 | | 1996 | 7.1871036971999 | | 1995 | 15.74223050216 | | 1994 | 8.154231285871 | | 1993 | 12.089792286898 | | 1992 | 13.637424171722 | | 1991 | 19.748544819558 | | 1990 | 16.756374707769 | | 1989 | 21.261867088608 | | 1988 | 17.66348615313 | | 1987 | 19.693593314763 | | 1986 | 23.864289821737 | | 1985 | 12.106756059825 | | 1984 | 17.036366379961 | | 1983 | 16.079873883342 | | 1982 | 14.823008849558 | | 1981 | 10.31728422454 | | 1980 | 20.819224932422 | | 1979 | 9.9043605123113 | | 1978 | 11.078100382614 | | 1977 | 12.732162792989 | | 1976 | 10.317415887741 | | 1975 | 9.6696954815125 | | 1974 | 10.024317751648 | | 1973 | 5.1121840390876 | | 1972 | 2.1023633461011 | | 1971 | 3.140421713942 | | 1970 | 3.7628985958054 | | 1969 | 3.4098202824374 | | 1968 | -1.6757594245691 | | 1967 | 0.70189748435374 | | 1966 | 9.0364406581763 | | 1965 | 14.839004461624 | | 1964 | 3.6609829488547 | | 1963 | 0.74664570813543 | | 1962 | -3.0030765879078 | | 1961 | 0.69360675493533 | | 1960 | 0.33282904709175 |
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