| Year | Value | | 2022 | 5.2532392221524 | | 2021 | 4.483590140424 | | 2020 | 4.8716739856556 | | 2019 | 3.928672909396 | | 2018 | 4.3744892145316 | | 2017 | 5.4220456802383 | | 2016 | 6.6737288135593 | | 2015 | 5.9959577812711 | | 2014 | 5.2221172022684 | | 2013 | 4.9603174603175 | | 2012 | 4.5372050816697 | | 2011 | 4.4408340102897 | | 2010 | 6.0136089356786 | | 2009 | 6.9183253260122 | | 2008 | 10.761418232683 | | 2007 | 0.91135045567524 | | 2006 | 2.3684623841683 | | 2005 | 1.7808043992583 | | 2004 | 2.1589313126695 | | 2003 | 14.709077966356 | | 2002 | 11.799447097261 | | 2001 | 9.2981733278397 | | 2000 | 15.595893310753 | | 1999 | 14.93218174077 | | 1998 | 13.574191765681 | | 1997 | 3.9643780522841 | | 1996 | 11.624178290845 | | 1995 | 17.280932681459 | | 1994 | 2.8527221738713 | | 1993 | 4.9741143031165 | | 1992 | 4.3096145700975 | | 1991 | 6.9656812776075 | | 1990 | 6.9533615990307 | | 1989 | 4.4804455132266 | | 1988 | 5.4450820766046 | | 1987 | 3.3374706936972 | | 1986 | 5.4537521815008 | | 1985 | 3.7104072398191 | | 1984 | 7.4206092035479 | | 1983 | 7.9020979013986 | | 1982 | 5.5350553505535 | | 1981 | 8.0542264761411 | | 1980 | 12.064343163646 | | 1979 | 5.7655954631935 | | 1978 | 5.7999999989996 | | 1977 | 4.5285820346223 | | 1976 | 7.6566496162451 | | 1975 | 10.490992582377 | | 1974 | 23.167283010325 | | 1973 | 8.3431534294722 | | 1972 | 6.0749999995151 |
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