| Year | Value | | 2022 | 20.953969729969 | | 2021 | 9.3301441083521 | | 2020 | 8.6255146965055 | | 2019 | 9.3708360560567 | | 2018 | 12.420178108921 | | 2017 | 11.543393918877 | | 2016 | 21.71111321365 | | 2015 | 21.867347554255 | | 2014 | 23.792064946969 | | 2013 | 27.283333333333 | | 2012 | 21.271265001378 | | 2011 | 7.6228226284852 | | 2010 | 7.4115909288383 | | 2009 | 8.4220442769666 | | 2008 | 8.7126018660904 | | 2007 | 7.9522099086403 | | 2006 | 13.974294354839 | | 2005 | 15.41034466043 | | 2004 | 11.429806082212 | | 2003 | 9.5767978691921 | | 2002 | 14.74463461016 | | 2001 | 22.7 | | 2000 | 29.581488463168 | | 1999 | 44.804164286167 | | 1998 | 29.748651282826 | | 1997 | 9.1373524300349 | | 1996 | 37.602045023502 | | 1995 | 83.325774754346 | | 1994 | 34.649636150832 | | 1993 | 22.772710233663 | | 1992 | 23.75135302304 | | 1991 | 12.615315382885 | | 1990 | 11.823538045415 | | 1989 | 12.446362050266 | | 1988 | 33.912164935434 | | 1987 | 25.155095428291 | | 1986 | 14.046867958764 | | 1985 | 10.518975993717 | | 1984 | 20.026303204233 | | 1983 | 13.502510517018 | | 1982 | 9.8211624443208 | | 1981 | 11.814697550021 |
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