| Year | Value | | 2022 | 7.1022312964853 | | 2021 | 2.3432835820895 | | 2020 | 5.3293507310171 | | 2019 | 2.7625201938611 | | 2018 | 2.3309637956687 | | 2017 | 3.0845262440355 | | 2016 | 0.84206908403506 | | 2015 | 2.4832687566044 | | 2014 | 0.79886383809702 | | 2013 | 1.4589337175792 | | 2012 | 1.3474036287766 | | 2011 | 0.8737931047811 | | 2010 | 2.7626946947735 | | 2009 | 4.2970657295536 | | 2008 | 4.8417132216015 | | 2007 | 3.9354838709677 | | 2006 | 2.0408163265306 | | 2005 | 1.199200532978 | | 2004 | 1.4189189189189 | | 2003 | 3.0162412993039 | | 2002 | 1.963567541992 | | 2001 | 3.5775545209507 | | 2000 | 2.5376884422111 | | 1999 | 1.9989748846745 | | 1998 | 3.2821598729486 | | 1997 | 2.8307022318998 | | 1996 | 0.90634441087622 | | 1995 | 2.2297013041649 | | 1994 | 2.3025607919087 | | 1993 | 3.5658569199912 | | 1992 | 4.0584415584416 | | 1991 | 6.4691358024691 | | 1990 | 4.7594412829797 | | 1989 | 7.748049052397 | | 1988 | 8.7602303728401 | | 1987 | 16.039395005276 | | 1986 | 4.7661413319776 | | 1985 | 1.0661528580604 | | 1984 | 5.5164001084304 | | 1983 | 1.6533480297603 | | 1982 | 6.6725455614345 | | 1981 | 26.845637583893 | | 1980 | 11.240149315636 | | 1979 | 4.1693670339167 | | 1978 | 6.4137931034485 | | 1977 | 5.7365094798246 |
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