| Year | Value | | 2022 | 5.7641231785227 | | 2021 | 3.4838805526668 | | 2020 | 1.28658490708 | | 2019 | 2.167730033054 | | 2018 | 2.7648313452879 | | 2017 | 1.8751005955255 | | 2016 | 3.55 | | 2015 | 2.1711366538953 | | 2014 | 2.0417028670721 | | 2013 | 2.1204862035311 | | 2012 | 0.69686411149836 | | 2011 | 1.2849515880915 | | 2010 | 2.41890639481 | | 2009 | 2.1973858685357 | | 2008 | 3.75393081761 | | 2007 | 0.7125890736342 | | 2006 | 2.3293498075754 | | 2005 | 1.5321336760925 | | 2004 | 0.45449850222084 | | 2003 | 2.4878255346178 | | 2002 | 1.2867252841518 | | 2001 | 3.0041970399824 | | 2000 | 3.0855060913128 | | 1999 | 2.3659673659673 | | 1998 | 2.2524132999642 | | 1997 | 2.5669233590026 | | 1996 | 1.262532491645 | | 1995 | 2.4603677869372 | | 1994 | 1.3756749807148 | | 1993 | 2.2882693319306 | | 1992 | 2.3280850491186 | | 1991 | 3.4381959910913 | | 1990 | 4.1310334831135 | | 1989 | 4.5461433550538 | | 1988 | 6.6763659877142 | | 1987 | 8.7170474516696 | | 1986 | 7.1764927481636 | | 1985 | 5.7148546395858 | | 1984 | 6.2182741116751 | | 1983 | 8.4652443220922 | | 1982 | 11.340996168582 | | 1981 | 13.642960812772 | | 1980 | 10.878661087866 | | 1979 | 4.5097276120621 | | 1978 | 8.1616715433962 | | 1977 | 9.103839711603 | | 1976 | 9.1614727654756 | | 1975 | 11.689223481685 | | 1974 | 9.4117681321189 | | 1973 | 7.419472836375 | | 1972 | 7.2584358296152 | | 1971 | 6.2238632350129 | | 1970 | 10.637206526418 | | 1969 | 2.9629495107521 | | 1968 | 3.4482932425421 | | 1967 | 4.57926975754 | | 1966 | 3.250563343053 | | 1965 | 4.18722443998 | | 1964 | 5.8670153875192 | | 1963 | 2.471610528965 | | 1962 | 5.2742595292073 | | 1961 | 2.1551727767092 | | 1960 | 0.36049234684462 |
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