Year | Value | 2022 | 17.347565107499 | 2021 | 18.712417613227 | 2020 | 17.393627484555 | 2019 | 16.228572290343 | 2018 | 16.160101045353 | 2017 | 16.726340984942 | 2016 | 16.604938556107 | 2015 | 16.776463112106 | 2014 | 16.745486101587 | 2013 | 17.961096290899 | 2012 | 18.886546102903 | 2011 | 19.709814586288 | 2010 | 19.51713712514 | 2009 | 18.772916773248 | 2008 | 21.048935882708 | 2007 | 21.728891044722 | 2006 | 21.475778085311 | 2005 | 19.581525048429 | 2004 | 19.779521836418 | 2003 | 18.725874350604 | 2002 | 18.420334415633 | 2001 | 16.836391106903 | 2000 | 17.462170960806 | 1999 | 17.075219743866 | 1998 | 17.571745781439 | 1997 | 17.756164160782 | 1996 | 17.822944841276 | 1995 | 17.488038508917 | 1994 | 18.597740909397 | 1993 | 18.528675443411 | 1992 | 17.963873009539 | 1991 | 18.250142715502 | 1990 | 19.155531356779 | 1989 | 24.99734012209 | 1988 | 22.196531103589 | 1987 | 21.370119132285 | 1986 | 17.944054291283 | 1985 | 20.888245056517 | 1984 | 18.865990535978 | 1983 | 17.173853419063 | 1982 | 17.634274968006 | 1981 | 19.693933041842 | 1980 | 20.514915429257 | 1979 | 20.166457898955 | 1978 | 20.29934940669 | 1977 | 20.919619993026 | 1976 | 21.366643997409 |
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