Year | Value | 2021 | 16.2870104126 | 2020 | 15.468042299388 | 2019 | 15.442186340932 | 2018 | 15.484417422625 | 2017 | 16.026136723629 | 2016 | 15.67745215657 | 2015 | 15.735383494934 | 2014 | 15.557192255196 | 2013 | 15.371170001028 | 2012 | 14.925159825418 | 2011 | 14.856162281001 | 2010 | 14.344637272663 | 2009 | 13.981294940625 | 2008 | 15.462035331737 | 2007 | 16.141635744402 | 2006 | 16.055889853904 | 2005 | 15.612445210697 | 2004 | 14.935601333 | 2003 | 14.872860761182 | 2002 | 15.182984424214 | 2001 | 16.330350174051 | 2000 | 16.706646218125 | 1999 | 16.283677542353 | 1998 | 16.117869893429 | 1997 | 15.851282527679 | 1996 | 15.389251578672 | 1995 | 15.081531602862 | 1994 | 14.525966788878 | 1993 | 13.947394583998 | 1992 | 14.058391239351 | 1991 | 14.427808657687 | 1990 | 14.39022432623 | 1989 | 14.469482378295 | 1988 | 14.489978918536 | 1987 | 14.716679911632 | 1986 | 14.344839718175 | 1985 | 14.329545847968 | 1984 | 14.078684409877 | 1983 | 14.231842218775 | 1982 | 14.894400602319 | 1981 | 15.008411377581 | 1980 | 14.707745499124 | 1979 | 14.466784495345 | 1978 | 14.303999948007 | 1977 | 14.370106627094 | 1976 | 13.89937214845 | 1975 | 13.793923917409 | 1974 | 13.985616140369 | 1973 | 13.53653536633 | 1972 | 13.827439350476 |
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