Year | Value | 2021 | 16.424180327869 | 2020 | 16.608606557377 | 2019 | 16.772540983607 | 2018 | 16.940114848236 | 2017 | 17.195159470824 | 2016 | 17.446070838761 | 2015 | 17.815177792601 | 2014 | 17.944165041568 | 2013 | 18.154291462238 | 2012 | 18.374267803926 | 2011 | 18.068731350962 | 2010 | 18.240740740741 | 2009 | 18.493715227694 | 2008 | 18.733890091762 | 2007 | 18.984729673958 | 2006 | 19.178364987613 | 2005 | 19.421786267424 | 2004 | 19.551745507127 | 2003 | 19.648760330579 | 2002 | 19.826428350036 | 2001 | 20.105437254497 | 2000 | 20.454074227659 | 1999 | 20.257101389177 | 1998 | 20.412606261663 | 1997 | 20.55774414265 | 1996 | 20.816918930127 | 1995 | 21.231598590089 | 1994 | 21.729214182044 | 1993 | 21.957287995024 | 1992 | 22.143893842007 | 1991 | 22.403068629484 | 1990 | 22.589674476467 | 1989 | 22.77628032345 | 1988 | 22.952519178934 | 1987 | 23.00435413643 | 1986 | 22.983620153431 | 1985 | 23.014721127929 | 1984 | 23.10802405142 | 1983 | 23.180592991914 | 1982 | 23.253161932407 | 1981 | 23.273895915405 | 1980 | 23.294629898403 | 1979 | 23.346464855899 | 1978 | 23.460501762389 | 1977 | 23.501969728385 | 1976 | 23.533070702882 | 1975 | 23.55380468588 | 1974 | 23.512336719884 | 1973 | 23.543437694381 | 1972 | 23.533070702882 | 1971 | 23.833713456355 | 1970 | 24.092888243832 | 1969 | 24.227659133319 | 1968 | 24.289861082314 | 1967 | 24.21729214182 | 1966 | 23.99958532034 | 1965 | 23.616006634875 | 1964 | 22.714078374456 | 1963 | 21.770682148041 | 1962 | 21.573709309558 | 1961 | 21.905453037528 |
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