Year | Value | 2021 | 18.293284717574 | 2020 | 18.646818915294 | 2019 | 19.2945982522 | 2018 | 19.687367355387 | 2017 | 20.276074775794 | 2016 | 20.799585622052 | 2015 | 20.713767338726 | 2014 | 21.340323367669 | 2013 | 21.461547557686 | 2012 | 22.018966993284 | 2011 | 21.882983997724 | 2010 | 21.718974321134 | 2009 | 21.894278547741 | 2008 | 22.067048677689 | 2007 | 22.156071951029 | 2006 | 22.2318807121 | 2005 | 22.491647638026 | 2004 | 22.699715622506 | 2003 | 22.910992861019 | 2002 | 23.264904313761 | 2001 | 23.622002998287 | 2000 | 23.914342019781 | 1999 | 24.23751799165 | 1998 | 24.759721739957 | 1997 | 25.285901875948 | 1996 | 25.710582794137 | 1995 | 26.105877436746 | 1994 | 26.572798285323 | 1993 | 26.992591577085 | 1992 | 27.438015871532 | 1991 | 28.212377562978 | 1990 | 28.898929079212 | 1989 | 29.472098274152 | 1988 | 30.108264291161 | 1987 | 30.770709191343 | 1986 | 30.918894427716 | 1985 | 30.752178226861 | 1984 | 30.76387175484 | 1983 | 31.058443142029 | 1982 | 31.772312629217 | 1981 | 31.520051752031 | 1980 | 30.864692088313 | 1979 | 30.809789153701 | 1978 | 30.995153966704 | 1977 | 31.304191428193 | 1976 | 31.807573873416 | 1975 | 32.847663880376 | 1974 | 33.618913901218 | 1973 | 34.739814958073 | 1972 | 35.476748339131 | 1971 | 35.888710174481 | 1970 | 36.797907699606 | 1969 | 37.150984613596 | 1968 | 37.788481025508 | 1967 | 37.567911043956 | 1966 | 38.148153745034 | 1965 | 39.275350513483 | 1964 | 39.96893393142 | 1963 | 41.503552059247 | 1962 | 39.930354769431 | 1961 | 34.513964522859 | 1960 | 35.455776123891 |
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