Year | Value | 2022 | 18.583147600011 | 2021 | 18.159924385009 | 2020 | 18.849728040064 | 2019 | 19.636914501153 | 2018 | 19.347732486376 | 2017 | 19.110374720054 | 2016 | 18.667693545628 | 2015 | 19.794720940223 | 2014 | 19.721013463213 | 2013 | 18.604639710506 | 2012 | 18.379291890792 | 2011 | 16.337329598985 | 2010 | 15.383257822255 | 2009 | 13.893051379238 | 2008 | 15.058811082695 | 2007 | 17.427949807313 | 2006 | 19.199748877727 | 2005 | 18.122454953128 | 2004 | 17.733164769422 | 2003 | 17.428726936812 | 2002 | 18.380851293892 | 2001 | 19.657274659967 | 2000 | 20.813343318339 | 1999 | 20.926097874168 | 1998 | 21.390497489756 | 1997 | 20.847651961459 | 1996 | 19.651122576867 | 1995 | 18.758936975547 | 1994 | 17.861705041527 | 1993 | 17.051004445686 | 1992 | 17.688024695694 | 1991 | 18.814188530315 | 1990 | 18.759265246655 | 1989 | 19.749360994615 | 1988 | 20.634866678456 | 1987 | 19.621355593934 | 1986 | 18.961025462532 | 1985 | 20.365666669509 | 1984 | 21.911040012998 | 1983 | 19.795417659364 | 1982 | 21.790130896417 | 1981 | 23.366773296631 | 1980 | 22.202864445438 | 1979 | 23.522142035288 | 1978 | 23.428484193096 | 1977 | 22.208196074024 | 1976 | 21.464579067498 | 1975 | 20.915256892974 | 1974 | 22.683357892577 | 1973 | 23.785934378017 | 1972 | 22.108810031975 | 1971 | 21.478301927287 | 1970 | 21.559429163992 |
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