| Year | Value | | 2022 | 43.488464174218 | | 2021 | 43.389016268151 | | 2020 | 30.59413903873 | | 2019 | 39.907345569778 | | 2018 | 18.014118337187 | | 2017 | 8.0449243766028 | | 2016 | 7.2454254895298 | | 2015 | 12.484681561153 | | 2014 | 16.606553235745 | | 2013 | 36.603035519103 | | 2012 | 27.256812724291 | | 2011 | 26.293385673861 | | 2010 | 10.089362928798 | | 2009 | 13.551554828151 | | 2008 | 25.410509031199 | | 2007 | 17.341040462428 | | 2006 | 10.015898251192 | | 2005 | 13.433118008508 | | 2004 | 14.761508697067 | | 2003 | 16.468011624479 | | 2002 | 14.33593373784 | | 2001 | 11.274247133212 | | 2000 | 14.476751318857 | | 1999 | 20.070707814687 | | 1998 | 17.86613421304 | | 1997 | 17.349225753871 | | 1996 | 28.937344016814 | | 1995 | 49.655985846275 | | 1994 | 31.447028423773 | | 1993 | 21.202630754776 | | 1992 | 25.807722616233 | | 1991 | 17.128567943401 | | 1990 | 7.6276749376393 | | 1989 | 22.34965304549 | | 1988 | 28.670634920635 | | 1987 | 28.571428571429 | | 1986 | 18.429003021147 | | 1985 | 4.3893409574154 | | 1984 | 12.540219453887 | | 1983 | 19.740189177861 | | 1982 | 18.689725926956 | | 1981 | 24.203589762449 | | 1980 | 20.64391443738 | | 1979 | 10.487236727349 | | 1978 | 11.721969204121 | | 1977 | 27.287784679309 | | 1976 | 11.256142506211 | | 1975 | 12.879181833834 | | 1974 | 14.248935538257 | | 1973 | 9.8194867331876 | | 1972 | 6.3982413512887 | | 1971 | 4.1952983726542 | | 1970 | 1.6668709397007 | | 1969 | 3.5931945155128 | | 1968 | 0.69036052199623 | | 1967 | 1.5976100796435 | | 1966 | 0.38814853215443 | | 1965 | 2.1543748352097 | | 1964 | 3.8144895722304 | | 1963 | 0.37184960722167 | | 1962 | 0.72132057165634 | | 1961 | 3.1625643958575 | | 1960 | 9.8224108129787 |
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