Year | Value | 2021 | 19.598181507442 | 2020 | 16.182407851665 | 2019 | 17.698893281943 | 2018 | 18.395524498411 | 2017 | 17.505794683077 | 2016 | 17.468964414004 | 2015 | 17.546082927147 | 2014 | 17.044501214415 | 2013 | 17.458772897196 | 2012 | 18.991059553699 | 2011 | 18.936095998996 | 2010 | 17.47100626721 | 2009 | 14.605860565337 | 2008 | 18.709265563015 | 2007 | 20.379028541213 | 2006 | 19.612017326691 | 2005 | 18.120889905945 | 2004 | 16.423945055057 | 2003 | 15.768827267037 | 2002 | 16.073067624173 | 2001 | 15.913125766804 | 2000 | 16.072403628139 | 1999 | 15.094957082375 | 1998 | 15.771289645011 | 1997 | 15.781100956555 | 1996 | 16.060542658901 | 1995 | 15.100753945571 | 1994 | 15.624744207471 | 1993 | 16.314589957786 | 1992 | 15.742889744911 | 1991 | 15.227963065361 | 1990 | 13.307384350169 | 1989 | 13.940364494898 | 1988 | 14.374031744122 | 1987 | 16.808316262064 | 1986 | 17.979503965044 | 1985 | 18.13121158086 | 1984 | 20.028187295002 | 1983 | 18.843454712441 | 1982 | 19.753498564766 | 1981 | 20.120586154547 | 1980 | 19.046623549746 | 1979 | 17.945358901759 | 1978 | 18.680814816142 | 1977 | 18.755773424635 | 1976 | 18.397754252898 | 1975 | 20.601154404257 | 1974 | 16.337951930124 | 1973 | 17.420500096103 | 1972 | 16.223271146831 |
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