| Year | Value | | 2022 | 8.2012899116172 | | 2021 | 1.8737832576248 | | 2020 | 0.13770757391651 | | 2019 | 0.6112469437653 | | 2018 | 1.1374876360039 | | 2017 | 1.2265331664581 | | 2016 | 0.09401665691575 | | 2015 | 0.038790399657973 | | 2014 | 0.24104742982676 | | 2013 | 1.2199934227431 | | 2012 | 3.0413633322677 | | 2011 | 2.7806327287932 | | 2010 | 1.5255160211825 | | 2009 | 0.77476813138738 | | 2008 | 3.3478325840102 | | 2007 | 1.829741122024 | | 2006 | 2.0908439101275 | | 2005 | 1.9852929852798 | | 2004 | 2.2067366142366 | | 2003 | 2.6725555277285 | | 2002 | 2.4653231917116 | | 2001 | 2.7851654271355 | | 2000 | 2.53768532095 | | 1999 | 1.6634599500771 | | 1998 | 1.9550855771938 | | 1997 | 2.0431077975014 | | 1996 | 4.0069766898104 | | 1995 | 5.235422580443 | | 1994 | 4.0518421806572 | | 1993 | 4.626734683313 | | 1992 | 5.2705899859293 | | 1991 | 6.2499992979029 | | 1990 | 6.456609061464 | | 1989 | 6.2598313795698 | | 1988 | 5.0582474766712 | | 1987 | 4.7472849038979 | | 1986 | 5.8235469186202 | | 1985 | 9.2059914425312 | | 1984 | 10.794496007681 | | 1983 | 14.646576674877 | | 1982 | 16.480414620221 | | 1981 | 17.969298751967 | | 1980 | 21.064168277075 | | 1979 | 14.798573566148 | | 1978 | 12.094013842507 | | 1977 | 17.13004878665 | | 1976 | 16.614166472579 | | 1975 | 16.950502566831 | | 1974 | 19.15976958547 | | 1973 | 10.79861745476 | | 1972 | 5.7495039373001 | | 1971 | 4.7916643833379 | | 1970 | 4.9683198732933 | | 1969 | 2.6572527338697 | | 1968 | 1.277313353908 | | 1967 | 3.7333383207382 | | 1966 | 2.3465889341332 | | 1965 | 4.5192683074346 | | 1964 | 5.9123225321859 | | 1963 | 7.454718225391 | | 1962 | 4.6911436074047 | | 1961 | 2.050697312787 | | 1960 | 2.3501614137705 |
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