Year | Value | 2022 | 16.729803296247 | 2021 | 17.459136378272 | 2020 | 14.703852777522 | 2019 | 15.688148312009 | 2018 | 14.253875130503 | 2017 | 14.990636695654 | 2016 | 12.484568248788 | 2015 | 12.924072017242 | 2014 | 12.700956048537 | 2013 | 11.913595846368 | 2012 | 12.914902905806 | 2011 | 14.302478171307 | 2010 | 13.410002436171 | 2009 | 11.902583034708 | 2008 | 13.708997932949 | 2007 | 14.9160651384 | 2006 | 15.265806427896 | 2005 | 15.993638451121 | 2004 | 15.472384423667 | 2003 | 16.118611294287 | 2002 | 16.38114170545 | 2001 | 16.524021658406 | 2000 | 16.588699101427 | 1999 | 15.955139781947 | 1998 | 17.480528909944 | 1997 | 16.229291736958 | 1996 | 15.726933889089 | 1995 | 15.522853432399 | 1994 | 16.650679153144 | 1993 | 14.496939706782 | 1992 | 14.649957840812 | 1991 | 15.663212940141 | 1990 | 16.349615327031 | 1989 | 17.626401993297 | 1988 | 17.911577703721 | 1987 | 17.734399551155 | 1986 | 17.495110626682 | 1985 | 18.693758457532 | 1984 | 19.177717780549 | 1983 | 18.880122990032 | 1982 | 18.236542030815 | 1981 | 18.398583773599 | 1980 | 19.641148004269 | 1979 | 21.24282523164 | 1978 | 22.124287894557 | 1977 | 21.769310879061 | 1976 | 20.621030926612 | 1975 | 19.311424901139 | 1974 | 20.063086639202 | 1973 | 22.924245876736 | 1972 | 22.111734492729 | 1971 | 23.457795880198 | 1970 | 24.462122982786 |
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