| Year | Value | | 2022 | 6.6570420275907 | | 2021 | 1.4019588396201 | | 2020 | 0.70596866133826 | | 2019 | 0.30338603659038 | | 2018 | 1.803916711419 | | 2017 | 0.75466324932362 | | 2016 | 1.6353111432706 | | 2015 | 1.5579071134626 | | 2014 | 0.44231005355705 | | 2013 | 1.8806546672409 | | 2012 | 1.2871224007922 | | 2011 | 0.9069249096918 | | 2010 | 0.99355740122639 | | 2009 | 0.97186299866764 | | 2008 | 3.7148431149406 | | 2007 | 2.0420851267334 | | 2006 | 3.2847616695481 | | 2005 | 0.98264166001595 | | 2004 | 1.4934440338177 | | 2003 | 1.1677336747759 | | 2002 | 2.7956196693694 | | 2001 | 0.61980187529798 | | 2000 | 1.8946345676346 | | 1999 | 0.68478260869564 | | 1998 | 2.7531133076448 | | 1997 | 1.0381989505161 | | 1996 | 2.9868092277302 | | 1995 | 6.1235816477552 | | 1994 | 5.1416715295336 | | 1993 | 5.183113960308 | | 1992 | 5.7402466286874 | | 1991 | 7.9861660079051 | | 1990 | 6.7825940151101 | | 1989 | 3.2599694922639 | | 1988 | 2.3690550548764 | | 1987 | 2.6987399771377 | | 1986 | 8.7335591870667 | | 1985 | 7.7286389008592 | | 1984 | 12.447569329185 | | 1983 | 6.2079353887031 | | 1982 | 10.527807297298 | | 1981 | 12.4925283921 | | 1980 | 9.4083794743796 | | 1979 | 8.3313654181546 | | 1978 | 9.7160327495434 | | 1977 | 12.597000992007 | | 1976 | 8.502152443493 | | 1975 | 7.9182892670274 | | 1974 | 17.556822745245 | | 1973 | 4.0846140361297 | | 1972 | 3.7591705572226 | | 1971 | 4.1553520683533 | | 1970 | 1.2791813237648 | | 1969 | 2.9498913543924 | | 1968 | 0.43647906904452 | | 1967 | 0.74827699389771 | | 1966 | -1.0135793646964 | | 1965 | 3.4828212200169 | | 1964 | 4.0215414742121 | | 1963 | 5.6997116874522 | | 1962 | 5.0967290813815 | | 1961 | 1.7631246049345 | | 1960 | 3.4242990654206 |
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