Year | Value | 2022 | 19.052705632564 | 2021 | 18.603169270869 | 2020 | 18.909632322158 | 2019 | 19.696467138888 | 2018 | 19.374763591406 | 2017 | 19.180180922187 | 2016 | 18.715399221381 | 2015 | 19.78216511826 | 2014 | 19.934795649767 | 2013 | 18.867167128853 | 2012 | 18.60293252325 | 2011 | 16.729920205852 | 2010 | 15.726276724035 | 2009 | 14.288089860605 | 2008 | 15.843310677253 | 2007 | 18.023574853463 | 2006 | 19.662283921155 | 2005 | 18.662834728672 | 2004 | 18.239226212833 | 2003 | 17.814210660889 | 2002 | 18.666343930792 | 2001 | 19.911547175488 | 2000 | 21.066170423537 | 1999 | 20.940594027563 | 1998 | 21.252503260922 | 1997 | 20.792078210958 | 1996 | 19.634938844144 | 1995 | 18.775214866034 | 1994 | 17.7866825586 | 1993 | 16.865976322509 | 1992 | 17.378009834313 | 1991 | 18.500683982668 | 1990 | 18.67394114643 | 1989 | 19.78258263085 | 1988 | 20.662710562671 | 1987 | 19.667923623321 | 1986 | 18.961537307673 | 1985 | 20.380054937377 | 1984 | 21.825750191609 | 1983 | 19.817361019037 | 1982 | 21.628757919694 | 1981 | 23.292094844238 | 1980 | 22.200099243088 | 1979 | 23.396574115609 | 1978 | 23.161315557988 | 1977 | 22.070797442844 | 1976 | 21.500367955842 | 1975 | 20.943019452558 | 1974 | 22.820338291369 | 1973 | 23.752642717279 | 1972 | 22.041354059562 | 1971 | 21.461979606696 | 1970 | 21.529766685037 |
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