Year | Value | 2022 | 17.419967694359 | 2021 | 18.833762327466 | 2020 | 17.322090141241 | 2019 | 16.049140194547 | 2018 | 15.996974125003 | 2017 | 16.417387108952 | 2016 | 16.216283120095 | 2015 | 16.332111947231 | 2014 | 16.853505973435 | 2013 | 17.566879429571 | 2012 | 18.230423242245 | 2011 | 18.932054321778 | 2010 | 18.48488007477 | 2009 | 18.195547126279 | 2008 | 19.999819135037 | 2007 | 20.565330064025 | 2006 | 20.145565922511 | 2005 | 18.162359272932 | 2004 | 18.729242612227 | 2003 | 17.913097214579 | 2002 | 17.54980126118 | 2001 | 15.871813872242 | 2000 | 16.28167415244 | 1999 | 16.188249777763 | 1998 | 16.812951234299 | 1997 | 16.542436239178 | 1996 | 16.618440833726 | 1995 | 16.784746117202 | 1994 | 18.277430209978 | 1993 | 18.470286135432 | 1992 | 17.683179296295 | 1991 | 17.755729120201 | 1990 | 18.419573505609 | 1989 | 25.566915995719 | 1988 | 22.433126064417 | 1987 | 21.48652509703 | 1986 | 18.252790302727 | 1985 | 21.465135854872 | 1984 | 19.199024794512 | 1983 | 18.527703724119 | 1982 | 18.725591972607 | 1981 | 20.366031329078 | 1980 | 20.77063796336 | 1979 | 20.328202788982 | 1978 | 20.83201535233 | 1977 | 21.256756709831 |
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