Year | Value | 2022 | 19.019962909296 | 2021 | 18.264394630822 | 2020 | 20.706233464179 | 2019 | 19.407438079468 | 2018 | 18.406048111477 | 2017 | 17.932644088855 | 2016 | 17.607791653635 | 2015 | 8.758005967653 | 2014 | 18.083856415995 | 2013 | 18.12260373969 | 2012 | 18.621707486796 | 2011 | 18.004518413898 | 2010 | 18.016713372322 | 2009 | 18.073013065712 | 2008 | 16.967219458653 | 2007 | 15.105461755175 | 2006 | 16.028671422802 | 2005 | 17.256387108996 | 2004 | 16.240267058843 | 2003 | 16.095327619903 | 2002 | 15.006548804181 | 2001 | 15.140801285537 | 2000 | 16.953664022797 | 1999 | 16.74865648796 | 1998 | 15.993362067028 | 1997 | 15.993484603997 | 1996 | 14.812987077639 | 1995 | 16.114216608414 | 1994 | 18.281506612777 | 1993 | 18.100627602386 | 1992 | 19.150289330768 | 1991 | 20.293441563829 | 1990 | 19.646805273834 | 1989 | 20.093165835187 | 1988 | 19.266115817732 | 1987 | 17.812732226901 | 1986 | 17.778172588833 | 1985 | 18.010590925502 | 1984 | 19.517409470752 | 1983 | 19.090339261929 | 1982 | 16.66012793177 | 1981 | 17.642276422764 | 1980 | 18.414395768656 | 1979 | 16.501308900524 | 1978 | 17.729306487696 | 1977 | 19.715178243293 | 1976 | 20.121173469388 |
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