| Year | Value | | 2020 | 2.0919588074578 | | 2019 | 2.3372267001303 | | 2018 | 2.6708283218659 | | 2017 | 2.8110184780906 | | 2016 | 3.1361073543679 | | 2015 | 2.5997198789962 | | 2014 | 1.9347146317087 | | 2013 | 1.8924603424623 | | 2012 | 2.6685018367001 | | 2011 | 2.4697353273462 | | 2010 | 1.8864911528196 | | 2009 | 3.1474605426663 | | 2008 | 2.8103510621811 | | 2007 | 3.8906948422277 | | 2006 | 4.2790226128451 | | 2005 | 7.6564126196408 | | 2004 | 6.2666634513163 | | 2003 | 4.2438346673742 | | 2002 | 3.9145394576632 | | 2001 | 4.0847201210287 | | 2000 | 2.9285316878256 | | 1999 | 3.4918628535314 | | 1998 | 2.3886584455909 | | 1997 | 2.5204281275176 | | 1996 | 2.2624970386164 | | 1995 | 4.6014158202524 | | 1994 | 4.4903636002384 | | 1993 | 2.5721315142026 | | 1992 | 3.199268738574 | | 1991 | 2.3082386363636 | | 1990 | 1.3379369874838 | | 1989 | 2.5376344086022 | | 1988 | 1.186943620178 | | 1986 | 1.6326530612245 | | 1985 | 1.3980868285504 | | 1984 | 0.79365079365079 | | 1983 | 0.66666666666667 | | 1982 | 0.26143790849673 |
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