Year | Value | 2021 | 19.893003687737 | 2020 | 19.477484028463 | 2019 | 19.295694177531 | 2018 | 19.113904326599 | 2017 | 18.932114475666 | 2016 | 18.750324624734 | 2015 | 18.984054433075 | 2014 | 17.140185945047 | 2013 | 17.140185945047 | 2012 | 17.140185945047 | 2011 | 17.140185945047 | 2010 | 18.802264582143 | 2009 | 18.802264582143 | 2008 | 18.802264582143 | 2007 | 14.802887861632 | 2006 | 14.740559912741 | 2005 | 16.236430686127 | 2004 | 15.514465278139 | 2003 | 15.228795512388 | 2002 | 15.841687009817 | 2001 | 16.096192801122 | 2000 | 17.254453851348 | 1999 | 17.695943489326 | 1998 | 13.94587856438 | 1997 | 15.259959486833 | 1996 | 16.709084298551 | 1995 | 15.981924894822 | 1994 | 16.506518464655 | 1993 | 16.007894873526 | 1992 | 15.810523035371 | 1991 | 15.441749337766 | 1990 | 16.059834830935 | 1989 | 16.070222822417 | 1988 | 16.090998805381 | 1987 | 16.122162779826 | 1986 | 16.137744767049 | 1985 | 16.153326754272 | 1984 | 16.174102737236 | 1983 | 16.184490728718 | 1982 | 16.194878720199 | 1981 | 16.205266711681 | 1980 | 16.210460707422 | 1979 | 16.215654703163 | 1978 | 16.220848698904 | 1977 | 16.226042694645 | 1976 | 17.275229834311 | 1975 | 17.285617825793 | 1974 | 17.290811821534 | 1973 | 17.031112034488 | 1972 | 16.771412247442 | 1971 | 16.771412247442 | 1970 | 16.350698592427 | 1969 | 16.553264426323 | 1968 | 17.664779514881 | 1967 | 16.786994234665 | 1966 | 16.267594660572 | 1965 | 16.267594660572 | 1964 | 15.753389082221 | 1963 | 15.753389082221 | 1962 | 15.233989508129 | 1961 | 15.233989508129 |
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