| Year | Value | | 2022 | 5.5181292857696 | | 2021 | 0.11543789441277 | | 2020 | 2.96354992076 | | 2019 | 1.6348554401228 | | 2018 | 3.4614748497375 | | 2017 | 0.488686760261 | | 2016 | 0.51248562626871 | | 2015 | 0.57446928635949 | | 2014 | 5.1659023792517 | | 2013 | 5.3913638858756 | | 2012 | 5.9120060249116 | | 2011 | 7.34270706018 | | 2010 | 1.0514816332104 | | 2009 | 7.0927171687629 | | 2008 | 17.320065196877 | | 2007 | 7.6660201348481 | | 2006 | 11.219987021415 | | 2005 | 7.330663416333 | | 2004 | 6.9858420268257 | | 2003 | 8.2694634933441 | | 2002 | 10.929634187269 | | 2001 | 6.9258373205743 | | 2000 | 7.8895618698672 | | 1999 | 8.0203683929684 | | 1998 | 12.399503812807 | | 1997 | 8.0840013548604 | | 1996 | 11.774356385664 | | 1995 | 9.6292197011623 | | 1994 | 13.256032591664 | | 1993 | 9.1686623332198 | | 1992 | 10.751160367529 | | 1991 | 15.050130775937 | | 1990 | 8.7375926184818 | | 1989 | 14.93224787103 | | 1988 | 16.737526572465 | | 1987 | 10.992366412213 | | 1986 | 13.571878940731 | | 1985 | 9.5682210708114 | | 1984 | 11.047180667434 | | 1983 | 6.2347188264058 | | 1982 | 12.983425414365 | | 1981 | 16.398713826366 | | 1980 | 13.090909090909 | | 1979 | 8.0550098231827 | | 1978 | 6.2630480167015 | | 1977 | 8.6167800453515 | | 1976 | 4.255319148936 | | 1975 | 10.069444444664 | | 1974 | 18.853171155599 | | 1973 | 3.2286995513524 | | 1972 | 6.8775461301553 |
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