| Year | Value | | 2022 | 4.5313452118211 | | 2021 | 6.5903025450664 | | 2020 | 6.5677300046232 | | 2019 | 5.4210059837645 | | 2018 | 5.1908547372878 | | 2017 | 5.6074453643334 | | 2016 | 5.8935194428814 | | 2015 | 5.0074693972269 | | 2014 | 3.5856184212801 | | 2013 | 3.2715318270165 | | 2012 | 3.4137415798137 | | 2011 | 3.5013972656875 | | 2010 | 3.7561481418781 | | 2009 | 3.9718063234108 | | 2008 | 3.0060727212151 | | 2007 | 3.5903267588688 | | 2006 | 3.5426457863214 | | 2005 | 4.343025941607 | | 2004 | 5.8044608858975 | | 2003 | 6.5439242503945 | | 2002 | 7.3991940702902 | | 2001 | 7.700626084897 | | 2000 | 7.1501486565456 | | 1999 | 7.5902238788879 | | 1998 | 8.7965597925757 | | 1997 | 8.0864758714549 | | 1996 | 10.292648471852 | | 1995 | 13.581581305237 | | 1994 | 13.259238782833 | | 1993 | 12.440219180204 | | 1992 | 31.786024447091 | | 1991 | 117.34982320869 | | 1990 | 48.517267267267 | | 1989 | 8.5398292034159 | | 1988 | 8.2366187424216 | | 1987 | 5.9762554147281 | | 1986 | 7.236209878916 | | 1985 | 6.4341085271318 | | 1984 | 6.7548638132296 | | 1983 | 6.830511260891 | | 1982 | 5.9542967492758 | | 1981 | 4.1270066770848 | | 1980 | 3.3139909735654 | | 1979 | 3.5485281259108 | | 1978 | 4.7607879924953 | | 1977 | 5.2936821322804 | | 1974 | 3.2791185729276 | | 1973 | 2.5249376558604 | | 1972 | 2.0389344262295 | | 1971 | 1.8921852387844 | | 1970 | 2.3927875243665 |
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