Year | Value | 2021 | 19.801636966562 | 2020 | 19.420586591234 | 2019 | 19.747182033606 | 2018 | 19.657019925582 | 2017 | 19.571173127822 | 2016 | 19.420211839117 | 2015 | 19.471487738407 | 2014 | 19.572219047936 | 2013 | 19.476072210645 | 2012 | 19.051244246043 | 2011 | 19.345868176761 | 2010 | 19.249256656386 | 2009 | 19.069106821914 | 2008 | 19.646967540069 | 2007 | 19.846309879618 | 2006 | 19.624508203716 | 2005 | 19.29183501517 | 2004 | 19.032896003719 | 2003 | 19.261284822373 | 2002 | 19.411333409005 | 2001 | 19.783880049543 | 2000 | 20.30872897184 | 1999 | 20.524481687236 | 1998 | 20.177376719014 | 1997 | 19.815172579301 | 1996 | 19.466457933899 | 1995 | 19.357238563395 | 1994 | 18.271628447188 | 1993 | 18.222619173128 | 1992 | 18.406791319235 | 1991 | 18.458238680216 | 1990 | 17.706584353531 | 1989 | 17.514761854241 | 1988 | 17.386381393795 | 1987 | 17.252580842325 | 1986 | 17.035103052175 | 1985 | 16.540834484413 | 1984 | 16.281037347673 | 1983 | 16.11887295448 | 1982 | 15.70947900116 | 1981 | 15.583590365904 | 1980 | 15.730309214315 | 1979 | 15.368262108507 | 1978 | 15.340467460204 | 1977 | 15.24389598964 | 1976 | 15.061414183197 | 1975 | 14.300318553751 | 1974 | 14.779930140334 | 1973 | 14.720782607146 |
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